problems with battery´s icon

Hallo, after installing sp1 in my hp compaq 6720s laptop with vista home

premium preinstalled, i

have observed the following problem:

Sometimes when i turn on the laptop or reinitiate it, the battery´s icon in

the notification area of the task bar, appears empty as it would be

discharged, which is not certain because it says 99% available, connected

and without charging. I used to solve the problem reinitiating the computer

because ticking in the battery icon in notification area of properties in

task bar doesn´t solve it.

¿Does anybody knows what is the cause of the problem and how to solve it

without reinitiating?

Thanks in advance

Regards

Clara