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Lithium Batteries - Life Cycles Vs Discharge Levels


Alan de Enfield

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I don't know if this has been posted before but it shows some interesting 'stuff' following research into Lithium batteries in Electric Vehicles.

 

From the table below it appears that you will get 'best life' by treating them similar to FLA's  and only using 50% of their capacity.

Effectively the only benefit is the re-charge time, but that has to be offset against the X times purchase price (5x, 10x ?)

 

BMZ GmbH – known for supplying batteries to StreetScooter electric vans – made some interesting tests on Samsung ICR18650-26F battery cells

 

....................The second chart is the most interesting one. In here we see how many charge/discharge cycles the battery cell can handle before reaching the EOL (End-of-Life) – 70 % of the initial battery capacity – in different scenarios.

 

  • Cycling from 100 to 0 % we get 500 cycles
  • Cycling from 100 to 10 % we get 500 cycles
  • Cycling from 100 to 20 % we get 1.000 cycles

 

  • Cycling from 90 to 0 % we get 1.500 cycles
  • Cycling from 90 to 10 % we get 1.500 cycles
  • Cycling from 90 to 20 % we get 2.000 cycles

 

  • Cycling from 80 to 0 % we get 3.000 cycles
  • Cycling from 80 to 10 % we get 3.000 cycles
  • Cycling from 80 to 20 % we get 3.500 cycles

 

  • Cycling from 70 to 0 % we get 5.000 cycles
  • Cycling from 70 to 10 % we get 5.500 cycles
  • Cycling from 70 to 20 % we get 6.000 cycles

 

As you can see it’s better to cycle battery cells at lower SOC. For example, if you decide to constantly fully charge a battery cell (100 %) and discharge it till 20 % you can expect 1.000 cycles until reaching the EOL. However, if you charge it till 80 % and discharge it fully (till 0 %), you can expect to triple the cycles (3.000) before reaching the EOL. In both cases you’re only using 80 % of the total battery cell capacity.

 

https://pushevs.com/2018/04/27/battery-charging-full-versus-partial/

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13 minutes ago, Alan de Enfield said:

I don't know if this has been posted before but it shows some interesting 'stuff' following research into Lithium batteries in Electric Vehicles.

 

From the table below it appears that you will get 'best life' by treating them similar to FLA's  and only using 50% of their capacity.

Effectively the only benefit is the re-charge time, but that has to be offset against the X times purchase price (5x, 10x ?)

 

BMZ GmbH – known for supplying batteries to StreetScooter electric vans – made some interesting tests on Samsung ICR18650-26F battery cells

 

....................The second chart is the most interesting one. In here we see how many charge/discharge cycles the battery cell can handle before reaching the EOL (End-of-Life) – 70 % of the initial battery capacity – in different scenarios.

 

  • Cycling from 100 to 0 % we get 500 cycles
  • Cycling from 100 to 10 % we get 500 cycles
  • Cycling from 100 to 20 % we get 1.000 cycles

 

  • Cycling from 90 to 0 % we get 1.500 cycles
  • Cycling from 90 to 10 % we get 1.500 cycles
  • Cycling from 90 to 20 % we get 2.000 cycles

 

  • Cycling from 80 to 0 % we get 3.000 cycles
  • Cycling from 80 to 10 % we get 3.000 cycles
  • Cycling from 80 to 20 % we get 3.500 cycles

 

  • Cycling from 70 to 0 % we get 5.000 cycles
  • Cycling from 70 to 10 % we get 5.500 cycles
  • Cycling from 70 to 20 % we get 6.000 cycles

 

As you can see it’s better to cycle battery cells at lower SOC. For example, if you decide to constantly fully charge a battery cell (100 %) and discharge it till 20 % you can expect 1.000 cycles until reaching the EOL. However, if you charge it till 80 % and discharge it fully (till 0 %), you can expect to triple the cycles (3.000) before reaching the EOL. In both cases you’re only using 80 % of the total battery cell capacity.

 

https://pushevs.com/2018/04/27/battery-charging-full-versus-partial/

The thing to look at is total delivered capacity to EOL, not just number of cycles:

  • Cycling from 100 to 0 % we get 500 cycles ==> 50000%
  • Cycling from 100 to 10 % we get 500 cycles ==> 45000%
  • Cycling from 100 to 20 % we get 1.000 cycles ==> 80000%
  •  
  • Cycling from 90 to 0 % we get 1.500 cycles ==> 135000%
  • Cycling from 90 to 10 % we get 1.500 cycles ==> 120000%
  • Cycling from 90 to 20 % we get 2.000 cycles ==>140000%
  •  
  • Cycling from 80 to 0 % we get 3.000 cycles ==> 240000%
  • Cycling from 80 to 10 % we get 3.000 cycles ==> 210000%
  • Cycling from 80 to 20 % we get 3.500 cycles ==> 210000%
  •  
  • Cycling from 70 to 0 % we get 5.000 cycles ==> 350000%
  • Cycling from 70 to 10 % we get 5.500 cycles ==> 330000%
  • Cycling from 70 to 20 % we get 6.000 cycles ==> 300000%

The really interesting point is that the total lifetime is still going up as the upper capacity drops to 70%, it would be interesting to know how far this carries on for. Maybe even something like 50% to 0% is the best choice?

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17 minutes ago, Alan de Enfield said:

From the table below it appears that you will get 'best life' by treating them similar to FLA's  and only using 50% of their capacity

That’s well known. However the difference in cycle life is remarkable. The well known Trojan T105 will give around 1200 cycles at 50% DoD, compared with 6000 cycles for a lithium from your charts above. So if keeping both types cycling over 50% of their capacity you’ll need to buy 5 sets of Trojans over that period. 

 

Of far more importance to boaters is the lack of sulphation with Lithiums. For maximum life a LA battery must be fully charged immediately following a discharge. Then if it’s going to be left a while it must have the charge regularly topped up (or left on float charge). Contrast that with a lithium at say 25% SoC which can be left for months at that charge state with no adverse affect. 

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1 minute ago, WotEver said:

That’s well known. However the difference in cycle life is remarkable. The well known Trojan T105 will give around 1200 cycles at 50% DoD, compared with 6000 cycles for a lithium from your charts above. So if keeping both types cycling over 50% of their capacity you’ll need to buy 5 sets of Trojans over that period. 

 

Of far more importance to boaters is the lack of sulphation with Lithiums. For maximum life a LA battery must be fully charged immediately following a discharge. Then if it’s going to be left a while it must have the charge regularly topped up (or left on float charge). Contrast that with a lithium at say 25% SoC which can be left for months at that charge state with no adverse affect. 

Something that struck me (probably more applicable to cars than boats).

You cannot charge lithiums at temperatures approaching freezing (I have seen +5*C as one suggested minimum).

 

You car battery is low, you park outside your house and 'plug-it-in', during the night there is a heavy frost and the temperatures hover around Zero - now what happens ?

 

Reading some articles, there appears to be some cars that are fitted with battery heaters (maybe a must for Scandinavia) but that seems rather a waste of power.

 

Personally I am not yet convinced that lithiums are at a stage on their product life cycle curve where I am ready to jump aboard. 

My 'lifestyle' seems to work fine with FLA's on the boat and Lithiums in my GPS, Phone, watch etc.

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It would also be interesting see what effect charging current has on lithium ion battery life.

 

The car manufacturers and public charge point providers are introducing ever more powerful chargers to reduce charging times and I wonder if this will result in shorter battery life, which of course benefits the manufacturers by selling more cars or replacement batteries.

 

 

Edited by cuthound
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4 minutes ago, cuthound said:

It would also be interesting see what effect charging current has on lithium ion battery life.

 

The car manufacturers and public charge point providers are introducing ever more powerful chargers to reduce charging times and I wonder if this will result in shorter battery life, which of course benefits the manufacturers by selling more cars or replacement batteries.

 

 

Agreed but the charge rates being used (up to 2C) are *far* higher than you'd ever see in a boat application. These rates do need things like battery cooling, but other than that don't have much effect on lithium batteries.

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3 minutes ago, cuthound said:

It would also be interesting see what effect charging current has on lithium ion battery life.

Just going by 'heresay' but I thought the benefit of these things was they would take 'as much as you can feed them', don't 'tail-off' so you get a quick charge.

 

I have also read that you can only do a 'fast charge' on an infrequent basis (so pull into the motorway services do a high-current quick charge whilst you have a cuppa) but then you cannot do another 'quick charge' for x number of 'normal charges'.

 

So much / many unknowns

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40 minutes ago, Alan de Enfield said:

Just going by 'heresay' but I thought the benefit of these things was they would take 'as much as you can feed them', don't 'tail-off' so you get a quick charge.

 

I have also read that you can only do a 'fast charge' on an infrequent basis (so pull into the motorway services do a high-current quick charge whilst you have a cuppa) but then you cannot do another 'quick charge' for x number of 'normal charges'.

 

So much / many unknowns

The links you gave in the OP are for Li ion batteries. That's not the same as LiFePo4's as most of us are using.

As Tony, says above, the biggest benefit of Li's is not having to get back to full.

 

On the charging side, you have to realise that 'fast' charging is what cars are doing....not narrow boats. We are not charging anywhere near as fast, or discharging nearly as fast. Yes, they will take everything you throw at them but that is much lower rates than what a car is doing. The key for me is that you dont have to charge to full ie much less running of engine, so then it will take as much as you throw at it.

Last year, my solar spent the bulk of its time on float, trying to feed full LA's. This year I get 20A all the time the sun is shining as I am only half full.

 

On the number of cycles, I dont think you can compare as the cycles on the Li's are done at much higher discharge.....and who does a cycle anyway? Mine bounces up and down 20%  ish SoC each day.

 

Finally, what do the number of cycles on an LA mean? If they are the claimed cycles when discharged and then charged on a defined basis, then most of the experience of boaters will be totally differnt. There are load of peeps on here who moan about cheapo's dying after 12 months. That is due to sulphation not cycles......and down to naff charging. Li's dont suffer that. LA's therefore can die due to excessive cycles and/or sulphation.

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2 minutes ago, Dr Bob said:

The links you gave in the OP are for Li ion batteries. That's not the same as LiFePo4's as most of us are using.

As Tony, says above, the biggest benefit of Li's is not having to get back to full.

 

On the charging side, you have to realise that 'fast' charging is what cars are doing....not narrow boats. We are not charging anywhere near as fast, or discharging nearly as fast. Yes, they will take everything you throw at them but that is much lower rates than what a car is doing. The key for me is that you dont have to charge to full ie much less running of engine, so then it will take as much as you throw at it.

Last year, my solar spent the bulk of its time on float, trying to feed full LA's. This year I get 20A all the time the sun is shining as I am only half full.

 

On the number of cycles, I dont think you can compare as the cycles on the Li's are done at much higher discharge.....and who does a cycle anyway? Mine bounces up and down 20%  ish SoC each day.

 

Finally, what do the number of cycles on an LA mean? If they are the claimed cycles when discharged and then charged on a defined basis, then most of the experience of boaters will be totally differnt. There are load of peeps on here who moan about cheapo's dying after 12 months. That is due to sulphation not cycles......and down to naff charging. Li's dont suffer that. LA's therefore can die due to excessive cycles and/or sulphation.

 

And you know this because you have had them for a few months....

 

All I am saying is that there are many unknowns about the long term use of lithium batteries in everything except iPods and phones. With wider adoption more knowledge will be gained and with wider understanding will come better and cheaper solutions.

 

With regard to cycles, certainly with lead acid batteries and I think also with lithium batteries, part cycles can be pro rata'd into full cycles, so if a battery has a life of 1000 cycles it will do 2000 or more half cycles etc. I accept that lithium batteries dont suffer sulphation, but they do cost considerably more even when purchased second hand and then need some form of battery management to prevent them self destructing under overcharge or deep deep discharge conditions.

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16 minutes ago, cuthound said:

 

And you know this because you have had them for a few months....

 

All I am saying is that there are many unknowns about the long term use of lithium batteries in everything except iPods and phones. With wider adoption more knowledge will be gained and with wider understanding will come better and cheaper solutions.

 

With regard to cycles, certainly with lead acid batteries and I think also with lithium batteries, part cycles can be pro rata'd into full cycles, so if a battery has a life of 1000 cycles it will do 2000 or more half cycles etc. I accept that lithium batteries dont suffer sulphation, but they do cost considerably more even when purchased second hand and then need some form of battery management to prevent them self destructing under overcharge or deep deep discharge conditions.

Yes I have only had them on the boat for 4 months and 2 months off grid.

but......

Of all the things I have bought for the boat, these Li's are the most effective spend! FOR US!

For the past two years, our routine on the boat, cruising all summer (6 months) and 3 days out of the marina in the other 6 months, has been dictated by having to fully charge the LA bank every few days. We were successful in this 'quest' with over 90% capacity left out of our cheapo's after 2 years. That routine was usually, boating in the morning maybe 3 hours or more, so we were not reliant on the solar to do the charging in the afternoon and only using  solar to top up. Not parking under trees. Limiting the amount of TV we watched and keeping an eye on usage. I was always concerned about stopping in one place more than a few days and in winter, did not like running our engine for 3 hours when moored up. Keeping the LA's full was a big imput into what we did on the boat and where and when we went.

This year is totally different. I dont do any of this anymore. Never think about how full the batteries are and whether I need to run the engine. It has just made life (full time on board) so much simpler. It really is chalk and cheese. So different to last year. Running the engine while mooring is now only to generate some hot water.

Will they last 2,3,5,10 years? Not a clue. The internet info seems to suggest they will last a while. At £1000 for 480Ahrs@13V, they are not that much more than a few Trojans. I am lucky that I can take financial risks and even if they only last a few years, the reduction in faffing is monumental ....FOR US.... (other peeps might be different). My guess is that they will be financially a good deal, especially as I reckon to reduce engine running by over 100 hrs in the year (and maybe 200), so that is good news for our neighbours.

2 hours ago, Alan de Enfield said:

 

Personally I am not yet convinced that lithiums are at a stage on their product life cycle curve where I am ready to jump aboard. 

 

Alan, what boat are you thinking of putting them on? There is no way I would dream of putting them on a lumpy water boat. The banging and crashing when beating would physically wreck them.....or dont you beat in your Cat?

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Tesla has acquired Maxwell Technologies and is intending to use Maxwell dry cell technology, much cheaper to produce and Elon Musk is talking of "million mile batteries" in production next year, effectively a battery for life. Watch this space. 

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43 minutes ago, cuthound said:

With regard to cycles, certainly with lead acid batteries and I think also with lithium batteries, part cycles can be pro rata'd into full cycles, so if a battery has a life of 1000 cycles it will do 2000 or more half cycles etc. I accept that lithium batteries dont suffer sulphation, but they do cost considerably more even when purchased second hand and then need some form of battery management to prevent them self destructing under overcharge or deep deep discharge conditions.

CH. Have a look at the graph of my SoC over the past month. I seem to be going up and down by 20% ish most days. I assume I will do this say 250 days a year. What do you think? How many cycles do you think that would represent?

I am not placing that much accuracy on the actual SoC number (from a BMV) but it does follow the amps in/out pretty well. I think it is likely reporting 5% too high and I can check this as I will have shore power for a few days this coming week and can get back to 100% to sync the meter for the first time since end April.

Screen Shot 2019-07-06 at 18.13.00.png

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21 minutes ago, Dr Bob said:

Alan, what boat are you thinking of putting them on? There is no way I would dream of putting them on a lumpy water boat. The banging and crashing when beating would physically wreck them.....or dont you beat in your Cat?

After the last 4 years of 'family medical problems' we should hopefully be able to set off on our grand-tour in the next year or so. We'll probably start taking a year or more going around the UK coast and then maybe Scandinavia and around to the Med.

 

I'm looking at the Cruiser rather than the Cat but if Lithiums won't take 'banging about' (the cruiser can be worse than the Cat) that puts them out of contention.

 

We'll be motoring most days so keeping the 1300Ah of FLA's charged up shouldn't be difficult.

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23 minutes ago, Dr Bob said:

Yes I have only had them on the boat for 4 months and 2 months off grid3.

but......

Of all the things I have bought for the boat, these Li's are the most effective spend! FOR US!

For the past two years, our routine on the boat, cruising all summer (6 months) and 3 days out of the marina in the other 6 months, has been dictated by having to fully charge the LA bank every few days. We were successful in this 'quest' with over 90% capacity left out of our cheapo's after 2 years. That routine was usually, boating in the morning maybe 3 hours or more, so we were not reliant on the solar to do the charging in the afternoon and only using  solar to top up. Not parking under trees. Limiting the amount of TV we watched and keeping an eye on usage. I was always concerned about stopping in one place more than a few days and in winter, did not like running our engine for 3 hours when moored up. Keeping the LA's full was a big imput into what we did on the boat and where and when we went.

This year is totally different. I dont do any of this anymore. Never think about how full the batteries are and whether I need to run the engine. It has just made life (full time on board) so much simpler. It really is chalk and cheese. So different to last year. Running the engine while mooring is now only to generate some hot water.

Will they last 2,3,5,10 years? Not a clue. The internet info seems to suggest they will last a while. At £1000 for 480Ahrs@13V, they are not that much more than a few Trojans. I am lucky that I can take financial risks and even if they only last a few years, the reduction in faffing is monumental ....FOR US.... (other peeps might be different). My guess is that they will be financially a good deal, especially as I reckon to reduce engine running by over 100 hrs in the year (and maybe 200), so that is good news for our neighbours.

Alan, what boat are you thinking of putting them on? There is no way I would dream of putting them on a lumpy water boat. The banging and crashing when beating would physically wreck them.....or dont you beat in your Cat?

 

I fully understand your reasons for getting Lithiums, and hope they continue work for you in the lo g term. I will probably follow suit when my 12 year old (still retaining 55% of original capacity) lead acid AGM's finally give up. 

 

Hopefully by then affordable plug and play Lithium systems will be available, even though they will have to live under the counter, where the extant batteries are.

 

14 minutes ago, Dr Bob said:

CH. Have a look at the graph of my SoC over the past month. I seem to be going up and down by 20% ish most days. I assume I will do this say 250 days a year. What do you think? How many cycles do you think that would represent?

I am not placing that much accuracy on the actual SoC number (from a BMV) but it does follow the amps in/out pretty well. I think it is likely reporting 5% too high and I can check this as I will have shore power for a few days this coming week and can get back to 100% to sync the meter for the first time since end April.

Screen Shot 2019-07-06 at 18.13.00.png

 

Assuming they pro rata like or better than lead acids, then they should last for st least 5 times the stated number of cycles.

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1 hour ago, Alan de Enfield said:

 

I'm looking at the Cruiser rather than the Cat but if Lithiums won't take 'banging about' (the cruiser can be worse than the Cat) that puts them out of contention.

 

The 'marine how to guy' raises the issue of mechanical reliability.

I dont think there is enough information .....at least I've not seen it.......out there to say LiFePo4's can withstand the 'banging about' you are going to get in an offshore cruiser. Certainly the ones with hundreds of small cells, so lots of soldered joints to break, look out of place in a lumpy water boat...but I would not even trust the Thundersky's I bought. Life in a canal boat is much much more sedate.

 

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Not lithium, but there are some interesting developments happening with lead-carbon batteries -- apart from the (expensive!) ones from Victron, Leoch, Northstar, they're starting to appear from reputable Chinese firms at what I guess will be much lower prices, for example:

 

http://www.ritarpower.com/battery/Energy Storage Battery/Lead Carbon/

 

As a replacement for flooded lead-acid traction cells (or lithium?) in big battery banks the 2V units look promising, they claim 5500 cycles at 30% DOD, 3400 cycles at 50% DOD, 2500 cycles at 70% DOD, 2000 cycles at 90% DOD which is about 50% longer than FLA (1500 cycles at 80% DOD) but with much better immunity to sulfation so better suited to PSOC applications like narrowboats. They also won't need the watering systems of FLA or the expensive/complex charge control systems of lithium.

 

The (smaller capacity, up to 225Ah) 12V cells have slightly lower lifetime but still pretty good (3000 cycles at 50% DOD, 2000 cycles at 80% DOD) and could be drop-in replacements for standard 12V batteries but with at least 2.5x longer lifetime (Trojans are 1200 cycles to 50% DOD). Yes I know all the usual provisos apply about Chinese batteries and inaccurate specification, but these look much more serious than most and are from a reputable (by Chinese standards) firm -- the attached spec is absolutely identical to the Victron 160Ah battery so I bet they're the supplier.

 

I wonder what their prices are without the (big?) Victron adder?

Ritar_DC12-175C.pdf

Edited by IanD
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45 minutes ago, IanD said:

Not lithium, but there are some interesting developments happening with lead-carbon batteries -- apart from the (expensive!) ones from Victron, Leoch, Northstar, they're starting to appear from reputable Chinese firms at what I guess will be much lower prices, for example:

 

http://www.ritarpower.com/battery/Energy Storage Battery/Lead Carbon/

 

ARitar_DC12-175C.pdf 411.25 kB · 1 download

The key questions for me are:

- do they have to be charged to 100% SoC?

- if so, what sort of power acceptance do they have compared to LA's .....ie do they have a long drawn out tail current period?

- It seems they are 'less' affected by sulphation......but are they immune to it?

 

Reading all the marketing info, they have many benefits but of course that info would never list the downsides (I wanted to say negatives). I wonder what they are?

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30 minutes ago, Dr Bob said:

The key questions for me are:

- do they have to be charged to 100% SoC?

- if so, what sort of power acceptance do they have compared to LA's .....ie do they have a long drawn out tail current period?

- It seems they are 'less' affected by sulphation......but are they immune to it?

 

Reading all the marketing info, they have many benefits but of course that info would never list the downsides (I wanted to say negatives). I wonder what they are?

If you look at the PDF I attached you can see what the tail current is -- still there but considerably smaller/shorter than standard LA. They're also happy to be charged at higher rates, 0.2C seems to be standard with 0.4C as the maximum.

 

All the articles (not just publicity) I can find on lead-carbon say that they're perfectly happy not to be charged to 100% (e.g. cycling between 30% and 70% SOC) with very little effect on lifetime -- they're being targeted at applications like hybrid cars where this is essential, they're designed for PSOC use.

 

Apart from size/weight (same as LA) the downside is that they're new and expensive from the marine suppliers (Victron, Northstar, Leoch), in spite of the fact that analysis suggests they cost less than 10% extra to manufacture compared to standard LA. Maybe once people realise they can get them straight from the OEM suppliers like Ritar the prices will drop?

 

All it needs is somebody who's interested to contact Ritar and ask them for prices including shipping to the UK, I've bought stuff direct from Chinese manufacturers before at a fraction of the EU reseller price with no problems, they're usually perfectly happy to ship direct to an end user in the UK. Or course you have to wait a few weeks for the ship to arrive, and any problems are down to you -- but given that they supply Victron, I wouldn't expect any quality issues.

Edited by IanD
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From the curve in the PDF I also worked out the "total lifetime capacity" figures (for the Victron-size 175Ah 12V battery) to compare with the lithium numbers further up:

 

90% DOD x 1800 cycles = 162000%

80% DOD x 2000 cycles = 160000%

70% DOD x 2250 cycles = 157500%

60% DOD x 2600 cycles = 156000%

50% DOD x 3100 cycles = 155000%

40% DOD x 3800 cycles = 152000%

30% DOD x 3800 cycles = 150000%

 

[Trojan T105 50% DOD x 1200 cycles = 60000% = 600x the Ah rating]

 

So lifetime capacity is about 2.5x higher than T105, but DOD makes almost no difference -- from 30% to 90% DOD lifetime capacity is between 1500x and 1620x the Ah rating. This is very nice for narrowboats, it means the lifetime hardly varies no matter how you treat them, and is likely to be more than 10 years even with heavy use.

 

For lithium-ion cells the numbers Alan found vary between 450x (90% DOD) and 3500x (70% DOD) the Ah rating, so very dependent on how the battery is treated -- especially how long it spends fully charged which lithium-ions don't like. I don't know how LiFePO4 cells compare to this, it's much harder to find such information -- could be better/similar/worse.

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It will be interesting to see how they fare in "real life".

 

I think we will find out sooner than for Lithium ion batteries, because:

 

i) they are cheaper,  and ,

 

ii) they don't require any changes to the boat and its charging systems.

 

 

Edited by cuthound
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On 06/07/2019 at 18:11, nb Innisfree said:

Tesla has acquired Maxwell Technologies and is intending to use Maxwell dry cell technology, much cheaper to produce and Elon Musk is talking of "million mile batteries" in production next year, effectively a battery for life. Watch this space. 

Tesla already have battery packs above half a million miles so they are pushing the boundaries, but this is the benefits of having a full proper battery management system on board.

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From my point of view, I dont ever expect to replace my batteries [Valence LifePo4] In my case my domestics are in the boat so they never get close to 0 degrees C, and the drive batteries live where the engine lived, sitting on plastic sheets and this winter they were always above 4-5 degrees

Now I paid 300 squids each ish secondhand with under 100 cycles, I never charge above 80% and they only go down to 50%, my drive batteries are stored at 60% when not in use and in normal use they are between 65% and 80% I have no fast charging and under normal use no fast discharging, as I said they should last my lifetime, so in a way they are a bargain

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5 hours ago, IanD said:

Not lithium, but there are some interesting developments happening with lead-carbon batteries -- apart from the (expensive!) ones from Victron, Leoch, Northstar, they're starting to appear from reputable Chinese firms at what I guess will be much lower prices, for example:

 

http://www.ritarpower.com/battery/Energy Storage Battery/Lead Carbon/

 

As a replacement for flooded lead-acid traction cells (or lithium?) in big battery banks the 2V units look promising, they claim 5500 cycles at 30% DOD, 3400 cycles at 50% DOD, 2500 cycles at 70% DOD, 2000 cycles at 90% DOD which is about 50% longer than FLA (1500 cycles at 80% DOD) but with much better immunity to sulfation so better suited to PSOC applications like narrowboats. They also won't need the watering systems of FLA or the expensive/complex charge control systems of lithium.

 

The (smaller capacity, up to 225Ah) 12V cells have slightly lower lifetime but still pretty good (3000 cycles at 50% DOD, 2000 cycles at 80% DOD) and could be drop-in replacements for standard 12V batteries but with at least 2.5x longer lifetime (Trojans are 1200 cycles to 50% DOD). Yes I know all the usual provisos apply about Chinese batteries and inaccurate specification, but these look much more serious than most and are from a reputable (by Chinese standards) firm -- the attached spec is absolutely identical to the Victron 160Ah battery so I bet they're the supplier.

 

I wonder what their prices are without the (big?) Victron adder?

Ritar_DC12-175C.pdf 411.25 kB · 7 downloads

 

4 hours ago, IanD said:

If you look at the PDF I attached you can see what the tail current is -- still there but considerably smaller/shorter than standard LA. They're also happy to be charged at higher rates, 0.2C seems to be standard with 0.4C as the maximum.

 

All the articles (not just publicity) I can find on lead-carbon say that they're perfectly happy not to be charged to 100% (e.g. cycling between 30% and 70% SOC) with very little effect on lifetime -- they're being targeted at applications like hybrid cars where this is essential, they're designed for PSOC use.

 

Apart from size/weight (same as LA) the downside is that they're new and expensive from the marine suppliers (Victron, Northstar, Leoch), in spite of the fact that analysis suggests they cost less than 10% extra to manufacture compared to standard LA. Maybe once people realise they can get them straight from the OEM suppliers like Ritar the prices will drop?

 

All it needs is somebody who's interested to contact Ritar and ask them for prices including shipping to the UK, I've bought stuff direct from Chinese manufacturers before at a fraction of the EU reseller price with no problems, they're usually perfectly happy to ship direct to an end user in the UK. Or course you have to wait a few weeks for the ship to arrive, and any problems are down to you -- but given that they supply Victron, I wouldn't expect any quality issues.

 

1 hour ago, IanD said:

From the curve in the PDF I also worked out the "total lifetime capacity" figures (for the Victron-size 175Ah 12V battery) to compare with the lithium numbers further up:

 

90% DOD x 1800 cycles = 162000%

80% DOD x 2000 cycles = 160000%

70% DOD x 2250 cycles = 157500%

60% DOD x 2600 cycles = 156000%

50% DOD x 3100 cycles = 155000%

40% DOD x 3800 cycles = 152000%

30% DOD x 3800 cycles = 150000%

 

[Trojan T105 50% DOD x 1200 cycles = 60000% = 600x the Ah rating]

 

So lifetime capacity is about 2.5x higher than T105, but DOD makes almost no difference -- from 30% to 90% DOD lifetime capacity is between 1500x and 1620x the Ah rating. This is very nice for narrowboats, it means the lifetime hardly varies no matter how you treat them, and is likely to be more than 10 years even with heavy use.

 

For lithium-ion cells the numbers Alan found vary between 450x (90% DOD) and 3500x (70% DOD) the Ah rating, so very dependent on how the battery is treated -- especially how long it spends fully charged which lithium-ions don't like. I don't know how LiFePO4 cells compare to this, it's much harder to find such information -- could be better/similar/worse.

I have looked at these for my electric truck, they seem the business its the weight that is the issue, my LifePo4s weigh 19 kilos and are 138ah the 55 kilos of the lead beasties will stretch my arms and flatten the suspension on the truck!!

But for a boat Ian they could be the bargain of the century as long as you can buy them well

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1 hour ago, WotEver said:

iii) They can operate down to negative Celsius. 

 

Good point.

 

How do our friends with DIY lithiums cope with this, other than by putting the  batteries inside a heated cabin?

 

What happens if they have to leave the boat in the middle of a cold snap and it is still below freezing when they return? Presumably wait until the boat warms up?

 

Do proprietary systems use the BMS to prevent the batteries being charged if The temperature is below 5°C? If so putting the batteries in the engine bay could work with lithiums on a leisure, rather than liveaboard boat.

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