Battery recovery from 11.2v ? (1 Viewer)

[Waveski]

Due to operator error and a coffee carton (don’t ask!) I managed to switch off the charger to the leisure batteries whilst the van is on EHU. The two 3 year old 100amp lead acid batteries are well looked after and have never previously been below 12.5 volts. When I finally twigged something was wrong the batteries were down to 11.2 v. The charger had probably been off for about 18 hours? All is now back on charge for the last 14 hours and things now look ok on my NASA BM-1 battery monitor; other than the available battery capacity looks low at 76%.
What is the likely long term damage that I have I done to the batteries and will they fully recover?

 

[Richard n Ann]

Due to operator error and a coffee carton (don’t ask!) I managed to switch off the charger to the leisure batteries whilst the van is on EHU. The two 3 year old 100amp lead acid batteries are well looked after and have never previously been below 12.5 volts. When I finally twigged something was wrong the batteries were down to 11.2 v. The charger had probably been off for about 18 hours? All is now back on charge for the last 14 hours and things now look ok on my NASA BM-1 battery monitor; other than the available battery capacity looks low at 76%.
What is the likely long term damage that I have I done to the batteries and will they fully recover?

Was the 11.2v figure under load? If so the standing voltage would have been much higher. Probably not as discharged as it first looks...

 

[Lenny HB]

If the charger has only been off for 18 hours you must have left something on drawing a fair bit of current around 10 amps, if everything was switched off I would say your batteries have had it.
If there was a 10 amp load on them 11.2v is OK as it's an under load voltage, but if no load 11.2 is beyond flat.

You could carry out a slow discharge test on them like this.

First charge the battery fully and leave it to settle for an hour then:-

For example if it's a 100a/h battery load it with a 5 amp load and run for 5 hours, this will represent a 25% discharge. (adjust load/time to suit the size of the battery)
Disconnect the load and leave to stand for at least 30 min then measure the voltage.
Repeat the test and you will have discharged the battery to 50%.
You can repeat again then it will be 75% discharged.

Always best to test each battery individually if in any doubt.

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[Waveski]

Yes the system was under a heavy load: compressor fridge, tv, heating and hot water, lights on, phone and iPad on charge. I knew something was wrong when the heating fan went off and the Truma system registered an error. So the batteries were getting near flat.
Thanks for your quick response, it’s given me hope!
Lenny, I’ll try your testing regime when I get back to home base. I’m away for another week but it looks like I won’t have an urgent problem.

 

[Bartyfixedit]

Discharged batteries fare best if you recharge them gently. You may well be ok.

 

[MitchandJenny]

I always have a C tech Charger with me just in case, which is hindsight and no help to you I know. Good leasure batteries 1 year old will come back up, as others have already said.
A drive will help a lot and I’m sure you will be more aware in future.
Happy travels.
Mitch.

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[PhilandMena]

If the charger has only been off for 18 hours you must have left something on drawing a fair bit of current around 10 amps, if everything was switched off I would say your batteries have had it.
If there was a 10 amp load on them 11.2v is OK as it's an under load voltage, but if no load 11.2 is beyond flat.

You could carry out a slow discharge test on them like this.

First charge the battery fully and leave it to settle for an hour then:-

For example if it's a 100a/h battery load it with a 5 amp load and run for 5 hours, this will represent a 25% discharge. (adjust load/time to suit the size of the battery)
Disconnect the load and leave to stand for at least 30 min then measure the voltage.
Repeat the test and you will have discharged the battery to 50%.
You can repeat again then it will be 75% discharged.

Always best to test each battery individually if in any doubt.

View attachment 539087

Would it not be better to fully charge the battery over a longer period say 36 Hrs, then disconnect it and leave it for two weeks and then measure the voltage to see if it has retained its full charge and then do the drop test you refer to. If its going to be tested after standing for only 1 hour after being charged its almost certainly going to be fully charged even if its capacity is largely used up. To test it after it has rested for much longer would start thee test in its true state of charge IMO.

 

[mitzimad]

Ive recovered batteries from below that you may find its best to jump another battery to it and then charge

 

[David and Sally]

Or maybe invest in an Optimate.

Amazon product ASIN B00ABG85QO

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[Gromett]

You may recover them, but I suspect they will be 'injured' and are likely to fail sooner than would have been the case.

Worth keeping an eye on them from now on.

 

[movan]

Havn't a clue about the technical aspect....

but mine have been that low for long period before now and recovered really well. That was some months ago.

Hope yours do too.

 

[ctc]

Discharged my 3 90ah Vartas to 11.0v on the display, several times and although 4+ year old still function nearly as good a new.

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[Lenny HB]

As I said it depends if you are reading on load or off load voltages, if off load it will damage the battery and they will lose capacity.

 

[Gromett]

As I said it depends if you are reading on load or off load voltages, if off load it will damage the battery and they will lose capacity.

A very important point. As Lenny HB says, You need to leave a lead acid battery disconnected for an hour or so for it's voltage to normalise. This is when to measure it.
Chances are if your battery is still connected it is pulling some load and the voltage will read lower than it actually is..

 

[autorouter]

I think the batteries are likely to be OK. There's two main worries - sulphation and damage due to the low voltage. If the voltage is very low, then there can be voltage differences between the six cells, and when it's recharged one of the cells can reverse. It looks like that hasn't happened.

Amorphous lead sulfate forms on the plates as part of the normal discharge process, and it turns back into lead/lead oxide when recharged. If the battery is left discharged, for a long time, the amorphous lead sulfate turns into crystals, which are almost impossible to turn back into lead/lead oxide. So the battery loses capacity. However this usually happens over several days, so 18 hours should be OK.

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