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How long to charge a dead battery?

Thanks to the unidentified phantom battery drain hidden somewhere in the deep recesses of my B250 camper van, my brand-new Costco Kirkland Signature battery went dead. I pulled it out of the van and put it on a 10-amp charger. It’s been charging for about 5 hours now, and the ammeter has dropped from the initial 10 amps or so down to the 1-2 amp range, though it’s hard to get an exact reading because the gauge has a pretty wide range, and the needle is close to zero. When I pull the charger clamps off and take a voltage reading, the battery shows 13.2 volts.

Is that enough of a charge, or should I leave it on overnight? I want to get a full charge but not cook the battery. It’s a 1000 amp/795 CCA lead/acid.

I could also switch chargers and put on a 1 amp trickle charger overnight, if that would be preferable.

Doesn’t your charger have instructions? I’d trust those over any guesses you might get here.

Yes, it would seem to be fully charged. If the caps are removable inspect the acid and if needed top it off with water up to the slots in the wells.

13.2 volts is a fully charged battery.


as the battery gets closer to been 100% charged the amps will drop down to zero more the cca more time to charge. a 10amp charger is the best it takes a little longer but it will not cook the battery ( an automotive battery ) Rod Knox makes a very good point about checking the water level in the battery if you can remove the caps please be carefull battery acid is very nasty keepa box of baking soda near by in case of a spill.

OK, thanks, Tester. Will call it good now at 13.2 volts.

You REALLY want to find out what is draining the battery…Starting batteries like the one you have do not tolerate deep discharges very well. They were not designed for that…it’s not something you want to keep doing…

Caddyman, I agree. From now on, I’m disconnecting the ground cable after each trip until I track that sucker down…

If this is a simple, non-automatic charger check the bat voltage while charging.
Shouldn’t let it run at or above 15V for any extended time.
An overnight charge at 14-14.5V is beneficial to reduce any minor sulfation.
Look up “equalizing charge”.

Don’t leave the charger hooked up to the battery overnight. My very old charger is a 10amp and when the needle drops about 1/2 from where it started I consider the battery charged. The instructions for the charger are long gone but I believe this was the recommendations of said instruction sheet.

Your charger might be newer and have better circuits and controls than my old one. If you can find the instruction sheet it should cover how long to reach a full charge. Since batteries differ based on age, size, capacity, etc. There is no “one” correct time. I’d rather error on the side of undercharging rather than “cook” a battery by overcharging it.

Thanks, Turbo. I couldn’t find a manual for the charger, so I erred on the side of not cooking the battery and charged it about 5 hrs on the 10 amp setting. Installed the battery in the van this morning, and it fired right up.

PS–I also found that battery drain…0.4 amps on the fused circuit that includes the (aftermarket) radio, so I pulled the fuse…not sure if the radio itself was the culprit or something else on that circuit, but the drain is definitely gone…