When you say it always shows this, what do you mean? How long have you let it sit like this? Does the computer ever run out of battery?
Also, what OS are you using? Is this the Windows battery monitor, or an HP one?
The battery monitor tells how much battery charge is remaining in the battery. If it is a big battery, it could sit at 100% for several minutes. Also, I'm not sure if this laptop uses a NiCd battery, but they suffer from the 'memory' effect which is where they think they have a full charge, but they really have a very small charge. Unfortunately, these computers generally can't be upgraded to Lithium Ion batteries.