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.
Anyway,
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
Ryan
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.
Anyway,
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
Ryan
