Keeping in mind battery life is warrantied for about 300 cycles at which they only will replace it if it's holding less than 50% charge the symptoms you are sharing look like an old battery. Is this battery over a year old?
I have Inspiron 3521 with the Radeon 8370M. When i start the laptop only on battery, the battery meter shows 5 hrs and there is no info message about starting up the Extended battery life option. Buuuut when i plug the charger for 1 minute and then unplug it, while the laptop is still working, suddenly Extended battery life is turned on and the battery meter(after 1 minute of recalculation) shows 6-7 hrs usage time. Aaaand this 6-7 hrs are real, i mean this is not some kind of bug or trick. Strange, cool or mystery?
I have aaaall of the latest drivers installed on the Win 7/64 system. Any suggestions why this happening every time?