Car battery

[David Lang]

My late wife's C3 has been on the drive since mid May this year, unused.

Not surprisingly the battery was flat. Central locking, dashboard lights etc all not working.

Bought a cheap charger from Wilkinson's & charged battery (out of vehicle). Checked it with a meter & it had slightly over 12v.

Put it back in the car, Central locking, dashboard lights etc all now working, but not enough juice to turn over the engine.

Do I assume the battery is now f*cked? Is it worth using jump leads now or should I replace the battery?

[Simon Mason]

I'm really sorry you lost Geraldine, Dave. :-( That's awful news.

[Tim+]

Very probably knackered, but, certainly worth trying some jump leads and seeing how it holds up once it's charged in the car.

Tim

[Huge]

IME, once car batteries have been run flat and allowed to sit that way for any length of time, they're knackered. You can restart the car with jump leads and the battery will give every appearance of working, except it won't hold charge for more a few hours.

Buy a new one. And a battery conditioner/trickle charger.

[Roger Mills]

If it had discharged to the point that the dash lights didn't work, it may well be f*cked.

But it would still be worth charging it a bit more. How long did you charge it for? A fully charged battery should show nearer 14v than 12. If your Wilko charger won't charge it any higher, try using jump leads to get the engine started, then drive it round and see whether the car's alternator can do any better.

[Huge]

Believe me, it's f***ed.

But don't stop the engine until you get home ....

[Fredxxx]

Agreed, David could solve all this nonsense and buy a new battery. I would recommend some float charger if the car is not going to be used for a month or so.

[RJH]

The battery on my (old) Honda Civic drained flat (I left an OBD thing plugged in for 2 weeks). Through 'dumb' charging (using a cheap Halfords charger) to get it up to 12V, then trickle charging using an Aldi charger for a week to 14V, the battery was fine for 6 months until I sold it.

That said, all consensus was that it would be ruined. I even bought a new battery on the assumption they were right - new Bosch battery for a Honda Civic anyone :-;

[Tim Lamb]

Worth trying a few charge/discharge cycles. Run the battery down using the car lights then re-charge. If it won't start the engine after a few cycles it is junk.

[ARW]

Or just leave the engine ticking over for 30 minutes - whilst attended..

[Fredxxx]

I can't disagree more.

A flat lead acid battery will generally only deteriorate when left discharged. Charging and recharging won't help. The best state to leave a battery is in a fully charged state.

Sulfation is a one way trip.

[Davey]

But the first time you need it somewhere on a cold night, it won't have enough oomph. Just replace it, and look after the new one.

[harry]

+1 Condolences.

[Robin]

Depends a bit on your plans for the car? If you selling privately or offering in part-exchange I'd be inclined to give it a go with jump-leads. And of course warming it up nicely before any prospective buyer tries it :) OTOH if it is going to a daughter...

PS

And my sympathies if, as so often, having to deal with such consequences is painful

[harry]

I have a car that is only used intermittently. I have fitted a quick disconnect to the battery to stop discharge and I either run the car once a week or give it a quick charge.

[Andrew]

My Astra handbook says disconnect the battery if the vehicle is not going to be used for more than 3 weeks (which seems alarmingly short).

Lead acid batteries generally don't like being allowed to go completely flat. All you can do is start it with jump leads and make sure the alternator is charging correctly (higher than 12 V across the battery teminals), and drive it around for half an hour or so. Should (could) be ok.

[Tim Lamb]

I can only speak from experience. More years ago than I care to remember, I was working at a Vickers Shipbuilding model tank. For open water trials models were powered by a stack of lead acid batteries.

The battery room had shelves of batteries around 45 amp/hr. capacity and mostly flat as your hat. My boss was of the same opinion as you *once flat = scrap*. The budget for the trial was pretty much petty cash as it was for a timber stern trawler being made at Berwick upon Tweed and certainly not MOD.

After a few charge/discharge cycles the batteries worked well enough for the performance trials at the Dumbarton test tank and open water demonstration at Berwick.

Trying won't cost anything other than time.

[Andrew Gabriel]

My engine management unit will lose the engine tuning if I do that, and spends first 5 miles relearning it. It's noticably rough for first half mile or so. I can't imagine it's particularly good for the engine to do this repeatedly.

[Simon Mason]

My battery went flat on a ferry after I forgot to disable the alarm. After I pushed it off in Rotterdam it spent the first 20 miles resetting the radio, air con etc.

[Dave Plowman (News)]

There are smart testers these days that tell you the actual battery capacity instantly. That is a good indication as to condition. Any decent battery place should have one.

If the battery was very low and the charger small it could take a long time to charge the battery. But as others have said if it was left flat, probably knackered.