battery issue

[wild weasel]

hello folks

i just have my first single coiler up and running

yesterday i started it up and it runs like a charm just humming away

now i have as a drive battery a 12v 225AH truck battery
battery on charge was a used car battery 12v 100AH

now in the first 4 hours i got it from 12v to 12.61 volt
this morning it was at 12.9v
at 2pm suddenly it was down to 10.5v

what happend here????
did i fry the battery ??? overcharged it????

thanks for anny suggestions

[Brodie Gwilliam]

well as long as the motor was running good and nothing shorted on you circuit, sometimes old batteries will go up at first and when they start to accept the charge will drop..... but that is a significant drop, its usually pretty slow and linear..... maybe that battery has a cell thats very close to being shorted and it shorted out.... you can tap the sides (close to the bottom) lightly with a hammer and that might break the cell from shorting

[Brodie Gwilliam]

you can tell how bad a battery is by hooking up a load, i use a 2 amp taillight, if it drops a volt or more then its probably going to be one of those batteries that climbs at first, then drops as it accepts charge...

these batteries will need to be charged and slowly discharged multiple times to make them good again, charge them tell the voltage isnt climbing anymore, then drain them to about 12v
some batteries will drop to 10v or so right off the bat, but start climbing while under load, keep loading tell the voltage stabilizes and it starts going down for a bit

[wild weasel]

ok brodie i give them another shot on the charge side
see what happens