for lead - acids cells floating level should be around 2,23 volts per cell on 20 degrees celsius. this is general rule for standing batteries, but for the cars it could be higher for few percents.
so: 2,23 X 6 cells = 13,38 volts. i guess you are doing fine with yours.
when we boost them, we load them to 2,4 volts per cell.
after capacity testing we charge them to almost 2,65 to 2,7 volts maximum. but this is only after deep charging ( 1,8 volts per cell with 10 hours 1/10 of nominal current). capacity you have on their walls is that type of data - for 10 hours discharge period with 1/10 of nominal current.
hope this was useful :-)
