my acer aspire 4736z laptop batteries are giving me a headache as they have an unpredictable standby time sometimes it konks off after just 10 mins of usage sometimes it runs for an hour the battery usage signal shows a discrepant reading it almost always when the systems shuts itself off due to low battery the reading still shows that more than 2 hrs of battery standby is still available. This problem has cropped up suddenly and almost every time the windows has to be resumed.
How old is the battery, they generally only last 3 -> 5 years some times even less. Alot depends on usage/charge-discharge cycles.
Might try this (2 x). Put a bootable DVD in laptop (ie UBCD) boot to CD, just leave untill battery dies then recarge over night, redo this a 2nd time. If this does not help then it's probably time for a new battery.