Sealed or open wet cell battery's?

[nicknorman]

So if I'm interpreting the discussion correctly, Then given the same use , two batteries are likely to last half as long as four batteries.

But a four battery bank is likely to cope with the occasional heavy load better. So there might be a slight advantage in the larger battery bank.

 

T C

 

Yes that's a reasonable analysis. And of course 2 batteries will spend more time at a lower SoC and hence lower voltage, possibly creating problems with things that like a good voltage such as fridges and inverters.

[by'eck]

 

Yes that's a reasonable analysis. And of course 2 batteries will spend more time at a lower SoC and hence lower voltage, possibly creating problems with things that like a good voltage such as fridges and inverters.

 

Another point I haven't thought through thoroughly, but given the two or four battery scenario and assuming the same Ah loss overnight, I wonder which bank will be fully re-charged the soonest, assuming same charger of course.

 

On one hand the two battery bank will be at a lower SOC so will be hungry for charge current, on the other this will be half that of four battery bank at same SOC. Run out of hands but a third consideration is that four battery bank although having the potential to draw twice the charge current, won't because its at a higher SOC.

 

First thoughts are that it will balance out so re-charge times will be similar. Whatever the answer it may have some relevance to bank capacity choice.

[nicknorman]

Another point I haven't thought through thoroughly, but given the two or four battery scenario and assuming the same Ah loss overnight, I wonder which bank will be fully re-charged the soonest, assuming same charger of course.

 

On one hand the two battery bank will be at a lower SOC so will be hungry for charge current, on the other this will be half that of four battery bank at same SOC. Run out of hands but a third consideration is that four battery bank although having the potential to draw twice the charge current, won't because its at a higher SOC.

 

First thoughts are that it will balance out so re-charge times will be similar. Whatever the answer it may have some relevance to bank capacity choice.

Presuming the charger is capable of putting out whatever current the batteries can take, the 4 battery scenario is bound to take less recharge time since each battery is starting at a higher SoC. If the charger is less powerful, it's anybody's guess depending on just how much oomph the charger can put out.

[dmr]

 

Another point I haven't thought through thoroughly, but given the two or four battery scenario and assuming the same Ah loss overnight, I wonder which bank will be fully re-charged the soonest, assuming same charger of course.

 

On one hand the two battery bank will be at a lower SOC so will be hungry for charge current, on the other this will be half that of four battery bank at same SOC. Run out of hands but a third consideration is that four battery bank although having the potential to draw twice the charge current, won't because its at a higher SOC.

 

First thoughts are that it will balance out so re-charge times will be similar. Whatever the answer it may have some relevance to bank capacity choice.

 

This last year Iv had 6 (675Ah) Trojans rather than the previous 4 so have thought about this stuff a little bit.

(tangent, one of the originals died after 3 years of hard use so I got 4 new ones and kept two old ones, wired as a slightly unbalanced a split-able bank)

 

There are three advantages

1 In normal "boating every day mode" the bank is at a higher SoC so should last longer.

2 In winter move once per week mode with a bit of care I can manage with running the engine only every other day.

3 It looks really cool!

I did think that charging the bank from a less discharged state would be slower (more time in absorption) but I don't think this is the case.

Gibbo had a rule (I think) that the current into a battery (in amps) is roughly equal to the amp-hours required to get to fully charged, so in fact it all balances out..

Only real issue is that when we get down to 50% or even less it takes a LOT of charging, lots of time in bulk mode. Could do with a bigger alternator but would hit all sorts of belt and pulley expenses.

 

...............Dave

[by'eck]

Presuming the charger is capable of putting out whatever current the batteries can take, the 4 battery scenario is bound to take less recharge time since each battery is starting at a higher SoC. If the charger is less powerful, it's anybody's guess depending on just how much oomph the charger can put out.

 

Yes sorry forgot to mention that charge source would need to supply as much current as battery banks could take, to make the comparison valid.

 

Add in the less wear and tear on batteries due to lower DoD and its a win, win situation in favour of larger bank.

[dmr]

 

Yes sorry forgot to mention that charge source would need to supply as much current as battery banks could take, to make the comparison valid.

 

Add in the less wear and tear on batteries due to lower DoD and its a win, win situation in favour of larger bank.

 

Gibbo used to say that no matter how you worked it out you always got the 50% answer (size the bank to aim for 50% discharge).

We all like big banks, are we missing something? or was Gibbo not really a god????

 

..............Dave

[by'eck]

 

Gibbo used to say that no matter how you worked it out you always got the 50% answer (size the bank to aim for 50% discharge).

We all like big banks, are we missing something? or was Gibbo not really a god????

 

..............Dave

 

Well the article on this subject refers to deep cycle batteries and references battery cost per amp hour used during their life cycle, and suggests aiming for a bank size that leaves them at 50% DoD after daily discharge.

 

I believe Nick's graph peaked at 60-70% DoD for max value in terms of cost per Ah used during the life of Trojan T105's. Interestingly this graph was a relatively flat between 30 and 80% DoD.

 

I suspect that many people will prefer to pay posssibly very little extra in the long term, for a larger bank and so have the comfort of not taking their investment to such high DoD, not to mention the potential for quicker recharge times.

 

Bottom line the 50% answer seems largely academic for deep cycle batteries.

[Graham.m]

I thought you were doing quite well until now.

 

Yep Your are quite right. Of course 50% is not the max you can discharge a battery too. Brain hurrying to get out of the door. What brain was trying to say is that 50% is the max that we should discharge our batteries to if we want batteries to have a long life.

 

I also think I said 50% charge was 10.5V, which shows where brain had gone, that is the total discharge voltage, 50% is of the order of 12.1 to 12.3 volts Like the 10.5v It is different depends on different batteries to many factors.

 

Only excuse I can give is hurrying to get out and on the way to collect the Christmas wine and was going to miss the tide. It was an interesting trip to Dieppe, glad I don't suffer mal de mer. Certainly blew the cobwebs away.

 

So lets correct 10.5/11V is total discharge 50% is the point at which to stop discharge if we want batteries to last.

 

Sorry for the delay but internet not available in the Channel

[Graham.m]

nicknorman, on 10 Nov 2015 - 1:58 PM, said:

The Peukert effect does exist. Let's say you have a 100Ah battery. You take 1A continuously. It's flat in 100 hrs. You take 100A, it's flat in perhaps 30 mins.

But then you go away for a while, come back and take 1A again, and you get the remaining 50 hours worth.

Once you define battery capacity tests as going from full, to a terminating voltage (as one does), you inevitably have Peukert because it's no good taking the 100A out for 30 mins and then saying "it's not really flat, it's just sleeping" because if you continue to discharge the voltage will plummet, and there will be some reverse biassing of cells going on. So Peukert is real, but only in the right context.

Yes it's a sweeping statement but equally, one which is correct to the best of my knowledge. Please read the doc that Richard linked to earlier, for a more comprehensive explanation. Consider first principles, how can it be anything else?

As I mentioned, I changed the Peukert exponent on the Mastershunt from 1.27 to 1 (so as an exponent, it then has no effect). This made no difference to the relationship between the MS SoC and the Smartgauge's. It only impacts the time to run. No I haven't fully discharged the batteries at high current, waited for them to recover etc. I do have some regard for their health!

 

There are two ways we can talk about batteries as they behave in a laboratory with highly accurate measuring equipment and controlled conditions or as they are on our boats with very variable measuring equipment, and a totally uncontrolled use conditions. This is a forum devoted to boaters, their boats and equipment and they look for information that helps them get the best they can out of their boats as economically as they can.

 

Batteries love being discharged at constant rates and charged slowly in controlled conditions. Unfortunately in our world that does not exist.

 

In the boating world batteries are used hard and the conditions vary greatly. Just looking at the temperatures over say, a day of cruising. Batteries tend to be in the engine bay, where their temperature is dependant on the temperature of the engine and the world at large. At the start of the day the temperature of the batteries with a cold engine will approximate that the world at large, that can be anything from freezing or below to 20C or more in high summer. Start the engine and the temperature in the engine bay starts to rise and the temperature of the batteries starts to rise with the heat from the engine and the charge being put in by the engine charging system. So we start from a situation where the temperature of the battery is rarely if ever the temperature that batteries are tested at in the labs 25/27C so the figures specified by the manufacturer in a lab are different in real life. Our boat batteries probably vary in temperature by 20/30C degrees in a 24-hour period, maybe more. Personally I have never measured it, just felt the difference in the engine room temperature over the day, from very chilly to nice and warm or even hot hot.

 

Batteries that would provide 100 percent capacity at 25/27C will typically deliver only 50 percent at –18C. As the temperature rises the battery recovers its ability to deliver its full capacity. Take the temperature up and the battery will deliver more capacity and current. Temperature affects the chemical reaction within the battery but also affect the life of the battery.

 

So we have a situation where our batteries are varying in temperatures, varying in load and charge, measured with instruments and using algorithms that are not of laboratory standard.

 

Where does that leave us? With batteries whose capacity varies with temperature, the rate at which they will take a charge varying. I can’t think of any battery parameter that is stable enough to allow us to take accurate enough measurements to prove any of the theoretical of battery chemistry.

 

Yes Peukert effect does exist but I would suggest that with all the other uncontrolled parameters the effect is not measurable on a boat.

 

The effect of a heavy discharge (one that is or the order of 25% or more of capacity) does have an effect on the overall capacity of the battery in that cycles. Yes some of the capacity will be recovered over time, but the extra energy that is used by the battery to deliver that heavy discharge is not. So yes you can discharge that battery heavily, the voltage will drop, stop the discharge and the voltage will recover. But does the battery recover to the stage where it would have been if that same number of Ahs had been drawn from the battery slowly. From lab work I have found the answer is no, the voltage is slightly down and so was the SG.

 

Yes there is lots of theory but how does that theory apply to batteries in boats. I would suggest that it does but in the boat it is very difficult to measure or categorise. So may I suggest our task is to give boaters advice and information that will allow them to get the best out of their batteries in terms they can apply to their boat.

 

Ed And of course to get it right and not have mental aberrations while hurrying to get a boat out of harbour

Edited November 11, 2015 by Graham.m

[nicknorman]

Yep Your are quite right. Of course 50% is not the max you can discharge a battery too. Brain hurrying to get out of the door. What brain was trying to say is that 50% is the max that we should discharge our batteries to if we want batteries to have a long life.

 

I also think I said 50% charge was 10.5V, which shows where brain had gone, that is the total discharge voltage, 50% is of the order of 12.1 to 12.3 volts Like the 10.5v It is different depends on different batteries to many factors.

 

Only excuse I can give is hurrying to get out and on the way to collect the Christmas wine and was going to miss the tide. It was an interesting trip to Dieppe, glad I don't suffer mal de mer. Certainly blew the cobwebs away.

 

So lets correct 10.5/11V is total discharge 50% is the point at which to stop discharge if we want batteries to last.

 

Sorry for the delay but internet not available in the Channel

 

Do you have a comment regarding my graph in post #115? I say "my graph" but of course it is really Trojan's graph, it is their data and the additional curve is just derived from their data without any interpretation on my part. It seems to be totally at odds with the view that one shouldn't discharge below 50%, popular with you and nearly everyone else.

[Graham.m]

Do you have a comment regarding my graph in post #115? I say "my graph" but of course it is really Trojan's graph, it is their data and the additional curve is just derived from their data without any interpretation on my part. It seems to be totally at odds with the view that one shouldn't discharge below 50%, popular with you and nearly everyone else.

 

The original graph from Trojan is almost certainly based on lab data and not real life. It does not specify the rate of discharge, for example the 20% DOD gives a life of 4000 cycles. Now that is discharged at what rate? The 100% DOD gives a life of nominally 750 cycle again what rate of discharge, level can be assumed as being Trojan's definition of flat.

 

There are two ways of looking at the Trojan graph base and left axis. That they discharged the battery as fast as possible in each case or they discharged the battery slow. I think you will find that the two methods of discharge would have different AHs delivered. Oh assumption is made that whatever rate was used it was a level rate. Also I note it is a graph developed for advertising so the conditions of the tests would have been highly controlled at best temp and discharge rate.

 

Am I correct that you have assumed that each discharge gave the DOD% of 225AH?

 

If your theory was correct your added line should be straight. I would suggest that is data needed in terms of rate of discharge, time, temperature, how the decision was made that the battery was at DoD x etc to make the data valid

 

Coming back to real life the variabilities are the problem.

[nicknorman]

The original graph from Trojan is almost certainly based on lab data and not real life. It does not specify the rate of discharge, for example the 20% DOD gives a life of 4000 cycles. Now that is discharged at what rate? The 100% DOD gives a life of nominally 750 cycle again what rate of discharge, level can be assumed as being Trojan's definition of flat.

 

There are two ways of looking at the Trojan graph base and left axis. That they discharged the battery as fast as possible in each case or they discharged the battery slow. I think you will find that the two methods of discharge would have different AHs delivered. Oh assumption is made that whatever rate was used it was a level rate. Also I note it is a graph developed for advertising so the conditions of the tests would have been highly controlled at best temp and discharge rate.

 

Am I correct that you have assumed that each discharge gave the DOD% of 225AH?

 

If your theory was correct your added line should be straight. I would suggest that is data needed in terms of rate of discharge, time, temperature, how the decision was made that the battery was at DoD x etc to make the data valid

 

Coming back to real life the variabilities are the problem.

Yes I have assumed each discharge gave the DoD% of 225AH. It couldn't really be done any other way, such as taking the DoD of the current actual capacity, since there is no way to measure the actual capacity without doing a full discharge cycle. Trojan consider the battery "dead" when it's down to 80% of capacity and it will be more or less spread over the life of the battery in much the same way for the different DoDs so the loss of capacity is not likely to skew the results significantly.

 

Of course, as you say, the real world is a bit different from lab tests in terms of temperature fluctuations and varying discharge rates. However it seems your line is that it must be these factors that explains the difference between the lab tests and your opinion. Which seems somewhat "clutching at straws" to me. So let me ask you, do you have any evidence at all to support your "don't discharge below 50%" rule, other than the ubiquitous hearsay, gossip and urban myth surrounding this point? People used to be sure the earth was flat too!

 

Oh and picking up in your penultimate para, no the line shouldn't be straight. Apart from inevitable experimental scatter, the DoD is surely bound to have some impact on total deliverable AH, it's just not what urban myth would have us believe.

Edited November 11, 2015 by nicknorman

[Graham.m]

Yes I have assumed each discharge gave the DoD% of 225AH. It couldn't really be done any other way, such as taking the DoD of the current actual capacity, since there is no way to measure the actual capacity without doing a full discharge cycle. Trojan consider the battery "dead" when it's down to 80% of capacity and it will be more or less spread over the life of the battery in much the same way for the different DoDs so the loss of capacity is not likely to skew the results significantly.

 

Of course, as you say, the real world is a bit different from lab tests in terms of temperature fluctuations and varying discharge rates. However it seems your line is that it must be these factors that explains the difference between the lab tests and your opinion. Which seems somewhat "clutching at straws" to me. So let me ask you, do you have any evidence at all to support your "don't discharge below 50%" rule, other than the ubiquitous hearsay, gossip and urban myth surrounding this point? People used to be sure the earth was lar, too!

 

Lets deal with the way to measure DoD, Do they specify it as being with reference to Ahs or Voltage or SG. I would suggest that a lab would normally use SG as it is the most accurate measure of charge in a battery and they are after life not most Ahs. Again they would temperature correct that.

 

As to 50% giving a non-deep cycle battery, leisure etc, years of experience in the industry has come to the conclusion that using a battery to 50% DoD maximum gives the best overall life and economy.From my own experience I have yet to prove them wrong and I have tried. If you remember I mentioned that temperature has a major effect on capacity such that you can have a 450Ah bank and if it is at low temperature its capacity is reduced. As most batteries in this country are rarely used at their optimum temperature 25/27C, their capacity is below that stated from the lab. Also bear in mind that at -18C a battery will only have about 50% of it capacity available (225Ah for the 450 bank) and therefore a battery discharged to 50% in that condition would be at its full discharge point. This is one of the reason you car batteries fail on a chilly winter's morning, and where if you wait for the sun to get on the car the car will start quite happily.

[by'eck]

We seem to be discussing deep cycle batteries exclusively, surely avoiding high DoD is far more relevant to leisure batteries than deep cycle. No one seems to have come up with a max DoD figure for them for best value/life so I'll stick a finger in the air and say max 30%, although almost by definition capacity will drop and force users to exceed this whether they like it or not towards end of batteries life.

 

Note this will speed their demise so you have no excuse not to replace them with nice new ones, whilst those with deep cycle ones may feel obliged to use them well (years?) after their capacity has dropped to say 50% from rated. Don't shoot me down in flames - its just a point of view

[Graham.m]

We seem to be discussing deep cycle batteries exclusively, surely avoiding high DoD is far more relevant to leisure batteries than deep cycle. No one seems to have come up with a max DoD figure for them for best value/life so I'll stick a finger in the air and say max 30%, although almost by definition capacity will drop and force users to exceed this whether they like it or not towards end of batteries life.

 

Note this will speed their demise so you have no excuse not to replace them with nice new ones, whilst those with deep cycle ones may feel obliged to use them well (years?) after their capacity has dropped to say 50% from rated. Don't shoot me down in flames - its just a point of view

 

:-) I don't think your finger in the wind is far wrong, but the main thing here to me is to be able to recharge the batteries in time available. It is acknowledge that the lower the DoD the longer a battery lives. To an extent it is a balancing act, but go too far and batteries are quickly damaged. As for replacing them I would suggest that if you start of with 20% and keep that level in Ahs your batteries would be down to a capacity in the area of 30% capacity before the need became desperate assuming warm weather.

[nicknorman]

We seem to be discussing deep cycle batteries exclusively, surely avoiding high DoD is far more relevant to leisure batteries than deep cycle. No one seems to have come up with a max DoD figure for them for best value/life so I'll stick a finger in the air and say max 30%, although almost by definition capacity will drop and force users to exceed this whether they like it or not towards end of batteries life.

 

Note this will speed their demise so you have no excuse not to replace them with nice new ones, whilst those with deep cycle ones may feel obliged to use them well (years?) after their capacity has dropped to say 50% from rated. Don't shoot me down in flames - its just a point of view

I think Trojans are not really deep cycle batteries, there are a 1/2 way house. It would certainly be interesting to repeat the graphing exercise with normal leisure batteries, I'll see if I can find any manufacturers' data.

 

By the way, did you mean DoD 30%, or SoC 30%? Surely not the former?

 

The rest I somewhat agree with in that most users don't have monitoring, or have only AH-counting monitoring and thus the end of life is accelerated by a tendency to go to increasing DoD to compensate for reduced capacity. Whether owners of deep cycle batteries are less prone to this, I don't know, but if one presumes they have deep cycle because they are interested in and understand batteries better than average, then you are probably right as a generalisation.

[nicknorman]

Lets deal with the way to measure DoD, Do they specify it as being with reference to Ahs or Voltage or SG. I would suggest that a lab would normally use SG as it is the most accurate measure of charge in a battery and they are after life not most Ahs. Again they would temperature correct that.

 

As to 50% giving a non-deep cycle battery, leisure etc, years of experience in the industry has come to the conclusion that using a battery to 50% DoD maximum gives the best overall life and economy.From my own experience I have yet to prove them wrong and I have tried. If you remember I mentioned that temperature has a major effect on capacity such that you can have a 450Ah bank and if it is at low temperature its capacity is reduced. As most batteries in this country are rarely used at their optimum temperature 25/27C, their capacity is below that stated from the lab. Also bear in mind that at -18C a battery will only have about 50% of it capacity available (225Ah for the 450 bank) and therefore a battery discharged to 50% in that condition would be at its full discharge point. This is one of the reason you car batteries fail on a chilly winter's morning, and where if you wait for the sun to get on the car the car will start quite happily.

So you are saying that you have no evidence to support a 50% figure, just a gut feeling and going along with what everyone else says (none of whom have any science to support their view). This is surely urban myth at its best! Although since we have shifted to leisure / starter batteries, I'll reserve judgement until I've repeated the graphing exercise with data from that type of battery.

 

As to the effect of temperature, this is similar to the Peukert issue. With a cold battery, the rates of chemical reactions are slower and thus, just like the inaccessibility of chemicals buried deep within the plates explains Peukert, the slow rate of chemical reaction in the cold means that during a standard capacity check (discharging to a specified terminating voltage) the terminating voltage will be reached much earlier. However, just like Peukert, the charge is only temporarily unavailable and once the battery is warmed, or if taking the current out very slowly, all the original AH can be extracted. If you disagree with this, please could you explain where the electrons liberated by each molecule of the chemical reaction go, if not to the -ve plate and thence around the circuit? Or do you think that cold electrons have less charge?

[by'eck]

I think Trojans are not really deep cycle batteries, there are a 1/2 way house. It would certainly be interesting to repeat the graphing exercise with normal leisure batteries, I'll see if I can find any manufacturers' data.

 

By the way, did you mean DoD 30%, or SoC 30%? Surely not the former?

 

 

To my mind DoD of 30% as mentioned = 70% SOC with reference in each case to the same battery bank capacity. If I have got the convention wrong apologies, but its how I have always understood it to be.

[nicknorman]

To my mind DoD of 30% as mentioned = 70% SOC with reference in each case to the same battery bank capacity. If I have got the convention wrong apologies, but its how I have always understood it to be.

 

Yes 30% DoD = 70% SoC. Ok so how do you correlate your suggestion of 30% DoD with the manufacturer's graph that shows the most lifetime AH can be extracted by going for around 60 to 70% DoD?

 

As something to throw in at this point, how about plate corrosion which seems to occur mostly at the end of the charge cycle as 100% SoC is approached? Lots of shallow cycles = more time spent charging near 100% SoC. Perhaps this is why, according to the manufacturer's data, this does not give the best overall extractable AH?

Edited November 11, 2015 by nicknorman

[Sea Dog]

As something to throw in at this point, how about plate corrosion which seems to occur mostly at the end of the charge cycle as 100% SoC is approached? Lots of shallow cycles = more time spent charging near 100% SoC. Perhaps this is why, according to the manufacturer's data, this does not give the best overall extractable AH?

Ah, so adding more batteries to the bank (or replacing with higher capacity) than is strictly necessary could also be a bad thing? Or at least it would be if we don't then charge less frequently?

 

Moral of the story: don't charge every x days if your batteries have capacity to stretch to x+1?

[nicknorman]

Ah, so adding more batteries to the bank (or replacing with higher capacity) than is strictly necessary could also be a bad thing? Or at least it would be if we don't then charge less frequently?

Moral of the story: don't charge every x days if your batteries have capacity to stretch to x+1?

I wouldn't go so far as to say that necessarily, it's just something to think about. As a counter to your points, leaving the batteries in a low SoC for long periods is also bad for them due to sulphation. Every time you use the batteries they are damaged, so it's just a matter of which factors are the more damaging and that depends on the specifics at the time - and something we can't easily quantify.

 

So the answer is probably to take the middle path and accept that batteries are a consumable!

[nb Innisfree]

Gibbo suggested keeping batteries out of the top 5% of SoC, or words to that effect, ie either keep them at 100% SoC or if they have to be discharged at all go below 95% SoC - or - either stop charging before 95% SoC is reached or go all the way to 100% SoC. Not having enough charging time to reach a true 100% being an unavoidable compromise.

[by'eck]

Yes 30% DoD = 70% SoC. Ok so how do you correlate your suggestion of 30% DoD with the manufacturer's graph that shows the most lifetime AH can be extracted by going for around 60 to 70% DoD?

 

As something to throw in at this point, how about plate corrosion which seems to occur mostly at the end of the charge cycle as 100% SoC is approached? Lots of shallow cycles = more time spent charging near 100% SoC. Perhaps this is why, according to the manufacturer's data, this does not give the best overall extractable AH?

 

Not disputing your first paragraph since I was referring to leisure batteries and your graph was for T105's.

 

Regarding the second point re lots of shallow cycles, that's pretty much what happens with a car battery. Funnily enough I was musing that very point whilst walking the dog - sad I know . Assuming a not unreasonable five year life for the average probably not branded battery on a car used everyday, we have something like 4000 light cycles during its life. I'm sure part of the ageing process involves some plate corrosion but I don't think my example supports your point.

 

If you can find the data needed though a similar graph of DoD v Ah supplied in lifetime for a typical leisure battery would be very interesting to see.

[by'eck]

Gibbo suggested keeping batteries out of the top 5% of SoC, or words to that effect, ie either keep them at 100% SoC or if they have to be discharged at all go below 95% SoC - or - either stop charging before 95% SoC is reached or go all the way to 100% SoC. Not having enough charging time to reach a true 100% being an unavoidable compromise.

 

I think the argument may have had some basis on jollying up the electrolyte given stratification and/or reducing sulphation that can otherwise occur with light use. My cheapo leisure batteries as fitted by builder are approaching the end of their life, but seem to find some hidden capacity reserve ironically when used hard, e.g. running micowave via inverter for a few minutes.

 

This is just a gut feeling but removing the surface charge and pulling some energy through the plates depth seems a reasonable explanation to me - there again it could be rubbish but how else do you explain this fact.

[nicknorman]

Not disputing your first paragraph since I was referring to leisure batteries and your graph was for T105's.

Fair enough, although in the context of your post:

 

"We seem to be discussing deep cycle batteries exclusively, surely avoiding high DoD is far more relevant to leisure batteries than deep cycle. No one seems to have come up with a max DoD figure for them for best value/life so I'll stick a finger in the air and say max 30%, although almost by definition capacity will drop and force users to exceed this whether they like it or not towards end of batteries life."

 

In the second sentence you refer to "them" without it being very clear whether "them" was deep cycle or leisure. I took it to mean the former but obviously that was wrong.