RE: Not Enough Battery?
125W divided by 12A = >10v. The readings don't tally. Also, 10-cells x 1.2v = 12v (Maybe you can get a bit more as a resting HOC voltage, but not 15v!) I can't see how you can expect readings of 15v even hot off the charger. If you are pulling ~12A from a pack of 1100mAh cells, you can expect voltage under load to drop considerably - to 9-10v.
Cheers, Phil