To check Battery charge Level

Hi:

I'm developping one Symbian app to check battery status. I have used ETELMM and Mobinfo API and battery charge level never change, I always get the same value.
I only get changes if I reboot the phone.

I use this methods (ETELMM) in Active Objects:

Phone.NotifyBatteryInfoChange(iStatus, iBatteryInfo);

iPhone.GetBatteryInfo(iStatus, iBatteryInfo);

The first method never wake up and the second always gets me the same value.

Can anyone explain me what happen??

Thanks

Pd: I have Series 60 phone (nokia 6670)