I would suggest charging the battery to 100% once and observing whether the problem persists.
For additional troubleshooting, you can try monitoring the battery current using a tool such as SystemDataScope and comparing it with the CPU suspend graph. If the CPU is suspended most of the time but the battery discharges quickly, this might indicate a hardware problem. If the CPU is not suspending enough, it is likely to be a software problem. If the current is inconsistent with the discharging rate, there is a problem with the calibration (or you have a faulty battery).