Battery questions.........

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I've had a varta battery sat in a bmw 116d for the best part of 10 months. When i removed it, it was showing 2.80v.

I have it on charge, which seems to be slowly charging. But im just wondering if 2.80v would be too low for it to recover properly? thoughts?.

Also another question..

I removed another 75ah 650cca battery from a diesel mini. If this battery mentioned above recovers, which is 80ah and 800cca, would it be ok to stick it in the mini?

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Le TVR said:

If its a Mini2, then you will probably lose the Stop/Start function. They have to reprogram the ECU with a battery change.

2004 mini one without stop start.

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PositronicRay said:

Most batteries have a 3 yr warranty, take it back. I had an internet cheapo fail after 30 months, the company just sent me another, no questions asked.

This was the original battery from a 2009 bmw 116d. So its 7 years old. It was working fine until i left it sit in the car for 10 months.

I know if i got 5 years out of a battery i'd be over the moon. But seen as the battery was good 10 months ago, i just want to know if charging from 2.8 volts would recover it. Or is it 50/50.

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GreenV8S said:

Batteries tend to fail one cell at a tie i.e. in roughly 2V increments. The usual failure mode for a cell seems to be the plates shorting and taking that cell to 0V. They can sometimes be recovered by zapping a high current through them to burn out the short but they're never the same after that.

I suggest that you've lost 3-4 cells there so the battery is scrap several times over. What you're doing now is probably charging the couple of 'good' cells back up. They'll soon be fully charged and will then be overcharged and start boiling as you over charge them trying to bring the overall battery up to voltage so you're likely ruin those too.

Thanks for that, i guess nothing to lose if i leave it on charge. If it does what you say then i'll have to scrap it.

Should know by tomorrow.

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Max_Torque said:

2 volts?

Yup, that'll be scrap.....

On another forum i've this moment read a chap saying that he said he recovered 0v batteries and worked for years. He also said he tried to recover a battery which showed 6v but wouldn't recover.

I guess its also down to the condition inside the battery rather than the voltage reading?.

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jas xjr said:

there are a few videos on youtube about restoring duff batteries. must be worth a look. seems to be about adding various householdchemicalsto the battery and then charging it.

That would be the older style batteries that are not sealed. I have topped them up with distilled water before and brought some back to life after a charge.

This battery in question is a sealed for life battery. So unable to top it up and must rely on charging only.

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Started the charging at 2.80v and now it is on 4.02v. So just over 1v charging every 24 hours LOL.

This will take 8 days or so...eeeek!

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GreenV8S said:

I suspect that means you have two cells which are good enough to come up to around their nominal voltage after charging, and the rest are dead. How many amp-hours of charge have you put through it now?

I tried a smart charger, but it seems they don't pick up the battery unless its on at least 8v i think. So i dug out a 15 year+ old absaar charger 11amp RMS and its been on for 27 hours and charged to 4.07v now.

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GreenV8S said:

Presumably it hasn't been running at 11A during that time, or you'd have boiled the electrolyte dry on the 'good' cells by now.

I still think it's a lost cause, but if you're determined to see some volts out of it and don't mind wasting your time I suspect your best bet will be to put a massive current through it for a fraction of a second. This is often enough to burn through the lead whiskers which are shorting the two plates together and allow the cell to start taking a charge again. Briefly connecting another car battery to it via heavy jump leads would be enough. I just mean a fraction of a second, not long enough to start smoking the leads, and if it doesn't work at the first go you're probably just making things worse (as well as damaging the other battery) by trying again.

Note that the two 'good' (it's all relative) cells are now in a completely different state to the rest of the battery so any current you put in to try to recover the bad cells is now overcharging (and damaging) the 'good' ones. The lower the current you use, the less damaging it will be.

It so happens i have another 12v battery sitting next to it which holds 12v but doesn't allow the car to crank.

So you say from the 12v battery connect + to - on the duff battery and so on? for a split second?.

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GreenV8S said:

I meant connect plus to plus and minus to minus - for about a quarter of a second, using decent jump leads. If it works then a cell that was previously shorted internally and stuck at 0V will slowly start coming up to voltage if you trickle charge the battery. As I said before - if it doesn't work at the first try it probably isn't going to work at all.

I stopped charging for around 12 hours, did the jump lead connection like you said for a split second. Then started charging again, but it hasn't moved off 4.44v for approx 7 hours now.

I guess thats confirmation that its a gonna.