What's the specific gravity of the cells on both batteries? Once a cell gets up to 1.265 or so, more charging doesn't do any good. Individual cells should be within 20 points of each other, like 1.250, 1.265, etc. The closer the better. If all the cells are above 1.250, the battery can be load tested effectively. Load the battery to 1/2 its Cold Cranking Amp (CCA) rating for 15 seconds. For instance, a 500 CCA battery gets loaded to 250 amps for 15 seconds. With the load still applied, the terminal voltage should not drop below 10.6 volts. Without a load test, other indicators of battery condition such as open circuit terminal voltage are pretty much worthless.
Jerry
