Mullered Batteries.

[nicknorman]

The only thing to bear in mind is that the charge is worth less at lower SoCs. So there is less energy in the bit between say 50% SoC and 40% SoC, than there is between say 100% SoC and 90% SoC. Quite a bit less. This is because the voltage is lower at lower SoCs and of course energy = voltage x AH. For some devices, the current drain will reduce at the lower voltages so you won't deplete the batteries any more quickly, but of course what ever it is is going to be less effective - eg incandescent lighting. Other devices are constant power - inverters, laptop/phone battery chargers, fridges, regulated LED lighting and to some extent a water pump, and they will thus sap more current and therefore drop the SoC faster at lower voltages / states of charge, than at higher ones.

[Lily Rose]

Thanks Nick, I hadn't appreciated that and it is certainly something I need to consider. Like I said earlier, we are managing at the moment but... the current batteries are still under a year old and we are still getting worthwhile input from the 200W of solar. My concern is that I have little contingency for when solar gets less effective and/or when the batteries are past their best. I was hoping that by switching to AGMs next I would have a bit more in hand, and therefore less to worry about on those (hopefully) infrequent occasions when the voltage may have dipped below 12.2 by morning.

Obviously I want to avoid spending some 5 times the cost of cheapos with little or no benefit.

[Tony Brooks]

Also remember that one AGM supplier suggest that you may need to "adjust" your alternator voltage to get 14.8 buta s adjustment is impossible in many cases then says you need to fit a Sterling A to B. These batteries are expensive enough already let alone close to another 300 quid so you can meet the suppliers demands.

[WotEver]

11 hours ago, Lily Rose said:

I was basing this on a conversation with the boss at Springwood Haven. He was of the view that AGMs are much more tolerant of being taken below 50% SOC thus effectively giving more usable AHs. I realise that this would have an impact on the number of expected life cycles.

For example

1,000 at 50% DOD vs 550 at 80% DOD according to the Tayna website for these...  https://www.tayna.co.uk/GPL-31T-Lifeline-AGM-Battery-P7243.html.

 

Wag is correct about (good) AGM's tolerance of deeper DoD which is also allied to my point about their resistance to sulphation. However as you yourself point out there is a somewhat severe reduction in cyclic life if it's something that you do regularly. If you balance that reduction in cycles against their higher initial cost you soon see that you don't get owt for nowt as my late father-in-law might have said. The whole point of the 50% 'rule' with wet lead acid cells is based upon exactly the same balancing act. 

[Lily Rose]

3 hours ago, WotEver said:

Wag is correct about (good) AGM's tolerance of deeper DoD which is also allied to my point about their resistance to sulphation. However as you yourself point out there is a somewhat severe reduction in cyclic life if it's something that you do regularly. If you balance that reduction in cycles against their higher initial cost you soon see that you don't get owt for nowt as my late father-in-law might have said. The whole point of the 50% 'rule' with wet lead acid cells is based upon exactly the same balancing act. 

It's not something I would do regularly, I hope, only on the hopefully infrequent occasions when the batteries did not get fully charged by the solar after a short-cruise day. Our leccy demand's are, and need to be, low. I don't intend to do anything to increase them. I would still aim to stay above 2.2 volts in order to make the batteries last as long as possible and therefore offset at least some of the higher cost.

I'm not looking to reduce the average annual cost of batteries but, at the same time, I'd like to avoid increasing it any more than I have to.

 

 

[WotEver]

1 hour ago, Lily Rose said:

I would still aim to stay above 2.2 volts...

Good move

(Yes, I know it's a typo)

[Naughty Cal]

27 minutes ago, WotEver said:

Good move

(Yes, I know it's a typo)

Can you get a 12v battery down to 2.2v?

[MtB]

On 09/09/2017 at 16:17, Naughty Cal said:

Can you get a 12v battery down to 2.2v?

 

Yes.

[OldGoat]

15 minutes ago, Naughty Cal said:

Can you get a 12v battery down to 2.2v?

 

4 minutes ago, Mike the Boilerman said:

 

Yes.

But not up again - that's the issue.....

[MtB]

On 09/09/2017 at 16:33, OldGoat said:

 

But not up again - that's the issue.....

 

You can if its a full traction battery...

[WotEver]

9 minutes ago, Mike the Boilerman said:

You can if its a full traction battery...

A full traction battery is only at 2.1V when fully charged

[cuthound]

1 hour ago, Naughty Cal said:

Can you get a 12v battery down to 2.2v?

Yes, and you can get it back up to 12 volts again, especially if you recharge it immediately. (You can even get batteries to reverse their polarity). 

The challenge then becomes one of getting it to keep its capacity in the long term. 

[Lily Rose]

3 hours ago, WotEver said:

 

(Yes, I know it's a typo)

Confirmed.

Just in case there was any doubt!

[WotEver]

1 hour ago, cuthound said:

Yes, and you can get it back up to 12 volts again, especially if you recharge it immediately. (You can even get batteries to reverse their polarity). 

The challenge then becomes one of getting it to keep its capacity in the long term. 

I recall a post from Gibbo where he'd taken a so-called leisure battery down to empty and that was that - it was broken and never worked again. 

[cuthound]

8 minutes ago, WotEver said:

I recall a post from Gibbo where he'd taken a so-called leisure battery down to empty and that was that - it was broken and never worked again. 

Depends in the rate  of discharge and quality of plate construction.

On a cheap leisure battery subjected to a heavy discharge the plates may buckle and short out, preventing recharge.

However many car starter batteries  (reputed to be rebadged as leisure batteries) have been completely flattened and successfully recharged, albeit with reduced lifespan.

[WotEver]

7 minutes ago, cuthound said:

many car starter batteries  (reputed to be rebadged as leisure batteries) have been completely flattened and successfully recharged, albeit with reduced lifespan.

I've flattened them myself more than once by leaving the lights on/door open/boot open. The latter two being very gentle discharges. They never last long after that. 

[cuthound]

34 minutes ago, WotEver said:

I've flattened them myself more than once by leaving the lights on/door open/boot open. The latter two being very gentle discharges. They never last long after that. 

Yup with batteries you generally get what you pay for.

However, as repeatedly pointed out on this forum, it is just as easy to wreck expensive batteries as it is cheap ones if you dont understand how to look after them.

Edited September 9, 2017 by cuthound
Spillung

[MtB]

2 hours ago, WotEver said:

I recall a post from Gibbo where he'd taken a so-called leisure battery down to empty and that was that - it was broken and never worked again. 

 

Yes but we all know Gibbo is fond of taking shades of grey and converting them to black and white. 

[WotEver]

3 minutes ago, Mike the Boilerman said:

Yes but we all know Gibbo is fond of taking shades of grey and converting them to black and white. 

He was contrasting it to a Rolls that he had on the bench at the same time which wouldn't die no matter how much he abused it. 

[MtB]

Just now, WotEver said:

He was contrasting it to a Rolls that he had on the bench at the same time which wouldn't die no matter how much he abused it. 

 

Like I said. He views things through a black and white filter.

I bet I could make the Rolls battery die.

[WotEver]

Okay Mike, whatever you say. 

[MtB]

Just now, WotEver said:

Okay Mike, whatever you say. 

 

I can 'break' them by relying on a SmartGauge to tell me when they are charged!

As you well know. 

Or are you claiming Rolls batteries would withstand my charging regime? I can't imagine Gibbo didn't think of trying to 'break' the Rolls by leaving it part charged for several days on end, repeatedly. 

[WotEver]

He was referring to discharging them down to 10.5V which is the context of this thread. 

[MtB]

1 minute ago, WotEver said:

He was referring to discharging them down to 10.5V which is the context of this thread. 

 

What ever you say, Tony.

[WotEver]

Just now, Mike the Boilerman said:

What ever you say, Tony.

I didn't say it, Gibbo did. 

He also pointed out that other makes such as Trojan also make 'proper' batteries which can cope with that kind of abuse. 

He then went on to say that despite this his personal preference was for cheap batteries that he replaces every 18 months because life's too short to obsess over batteries. But that of course is an opinion as opposed to a fact.