Battery and Starter Issues

[mclairmo]

Just installed a new mini starter but when I went to crank it, the pinion gear engaged the flexplate but would not turn the engine over at all, just makes a loud chattering sound. Checked the battery and it was under 12 volts. Have had my 2 amp charger on it for about 16 hours total and battery still will not measure past 12.5 volts. Battery is only 8 months old but has been discharged several times and recharged. Should my battery measure 12.6 volts or more? Could it be that the battery is dead/weak due to the discharging even though it is fairly new? It's a sealed battery and I do not have a load tester, just my multimeter. I was able to turn the flexplate by hand and get the pinion to disengage and go back into the starter. I properly shimmed the starter to obtain proper ring gear back lash (I used two shims) and the starter pinion to ring gear clearance was already acceptable. I am going to try to charge the battery one last time tonight to see if it will go past 12.6 volts. If not, I wil pull it out and exchange it and see if that helps. If not, I will have to pull the starter and bench test it to see if the pinion will spin. Any ideas? Thanks.