Totally discharged battery - dead?

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SimonA

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Went to the boat today and found I'd left the domestic battery connected last time and it had run totally flat, not even enought power to run a light. It's a 185ah leisure battery, the sealed type. Connected my electronic charger and it didn't even recognise the battery, so went out for a run in the boat for an hour. Reconnected charger and it came up with 11 volts in the battery and started charging at 13.7 volts.

Is it likely to be dead or can leisure batteries take that sort of abuse?
 
It depends on how long ago "last time" was. :)

If the answer is "2013" then it's probably dead.
If "last week" then it's worth trying to save. I would charge it for a bit using the charger, fire up the engines and let the alternator give it a good fast charge for a couple of hours, then plug the charger back in overnight.

.
 
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Some newer chargers won't recognise a flat battery nor an alternator excite to charge one. Ive managed to recover a 12v leisure battery registering 7V using a old " cheap" DIY garage charger to trickle charge enough in for a decent charger to take over. But tbh. The battery was never as good subsequently. Seemed to loose Ah capacity even though it could still hold charge. (Left a boat winterised on a trailer where a timed auto bilge pump bypassed the isolator)
 
it normally damages the battery if you drop it that low, so yes you could recover most of the charge but it will never be 100%. If you rely on it for domestics ect, and want to go cruising and stop for a while then i wouldn't depend on it personally but you may get away with it!
 
let the charger work for a day or so,
then disconnect all loads,
the battery should read at least 12,3V
if the voltage drops below that, after a few hours, the battery is bad.
the battery should keep 12,3V at least for a few day's (without any load on them)
 
Do you use (or can you set up the battery) for engine starting?

If so, and if your batteries do seem to recover, I would suggest cranking with them a bit (assuming they will be suitable). Not to take them too low, but to get some high current densities going through the cell's plates. It'll help get rid of some of the soft sulphation that may have formed and will improve the state of the battery a touch. Don't overdo it though! It's probably worth looking at the specs of the battery first, though, to ensure you won't end up over cranking and melting the lead-work that joins the cells together or joins the cells to the battery's terminals!

One thing to bear in mind though, if you are going to be charging batteries that are a bit suspect is http://www.ybw.com/forums/showthread.php?429538-one-battery-gone-bust

Don't let that scare you though! :)
 
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