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Charge 8 Volt (8V) Battery with 12V Charger?

91517 Views 2 Replies 2 Participants Last post by  mghardy
I've got a set of fifteen 8 volt US Battery 8VGC XC batteries purchased from a local supplier. The sales guy said they were special ordered with automotive terminal posts for another EV conversion, but the buyer backed out. I have an uneasy feeling that they may have been sitting in the warehouse for a while.

They each show about 8.25 volts. Is this an OK level?

I have a 1 amp 6V/12V motorcycle battery charger that I'm thinking of hooking up to the batteries individually just to keep them topped off so they don't have to sit idle any longer.

This thread ( mentions using the 6 volt setting, but I don't think that will have enough "push" to charge the 8 volts.

I've read on few other sites that using the 12V setting is OK as long as they don't have too many amps boiling the batteries over.

So the main question is: will briefly (30-60 minutes each) using the 12V charger setting on these 8V batteries hurt them?
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8.25v is fair but certainly not good voltage, my worn antiques end up around there. If they charge up correctly and hold at least 8.35 after sitting 24hrs they still have moderate capacity left. Not saying you can't use them lower, I do, but your range will be more limited and care will have to be taken so you don't damage any.

Also they are likely sulphated if that voltage is due to sitting an extended period, a desulphator, EDTA or simple old fashioned cycling of the batteries should bring them back fine if they are new and unused.

A simple suggestion, why not string them up to a standard 24v? You could then use either 2 dumb 12v car chargers or one smart 24v charger for the set.


I have an old Century multirate 6v/12v quickcharger at its 6vx10amp setting it is PERFECT for an 8v battery getting it up to roughly 9.2v which is fine for slow charging, this would definately overcharge a 6v battery, if you check the terminal voltage of the cheap DUMB rapid charging multirate 6v/12v car battery chargers you will find something similar on most, only a few charge a 6v battery safely.

As for a 12v charger on an 8v battery I can say that it sometimes can work to spot charge part way, but if you use a DUMB 12v battery charger you may repeat what I did blowing a lead off the charger. Even at 2amp usually you will drastically short out a 12v dumb charger and potentially damage the charger. The solution is to run the power through a car battery discharge tester or some sort of resistor. But it is VERY easy to overcharge the battery (I know as I tried a few times) and it is VERY easy to not get full charge afterword because the absorption faze is impossible. (unless you had a multirail charger and ran at 12vx2amp until the correct voltage was reached then flip it to the 6vx10amp setting to float and absorb.

The electronic cheapo battery chargers like the new black and decker BD-10 will keep their rate constant and work fine to partially charge a 8v battery but you can never get to the absorption faze since the charger won't ramp down and instead continues to beat the crap out of the battery.

I have heard of some reprogramming the new electronically controlled chargers to stop at different voltage curves but my guess is its above your and my head to complete without help.

Good Luck
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Very helpful comments, rmay635703. I put the 12V charger on one of the 8V batteries for 45 minutes, and it brought the charge up to 8.35 and it seems to be staying there. I decided not to try to go all the way with the charging yet. I will try your 24V smart charger idea as a way to do a few at a time, fully charged.

If anyone else has any thoughts on the matter, I'd love to hear that as well.
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