Open terminal, and then resize the window for a greater width (if you don't the result will be truncated).
Type:
ioreg -l | grep -i IOBatteryInfo
Should tell you your capacity of your battery. Mine is about 3000 for an 18 month old PB.
Wondering if it had "capacity" which can be filled.
Other things to do are to zap PRAM, reset PMU, reseat battery, and then if all fails read this
article
Hope all goes well...