I have a rather strange problem - I have a year old Acer Aspire 5745pg Core i7 laptop which up until January ran perfectly. In January I upgraded to Windows 8 and after about a day my laptop would shut down on battery after only 10 minutes (Prior to installing it would last 1.5 - 2 hours). I reinstalled Windows 7 using Acer backup cd's.
This is where my major problem has started, when i re-installed windows 7 I started getting the "Your battery needs changing" alerts with the red X (with the AC plugged in, the laptop ran fine though); however when on battery after 10 minutes the laptop would completely shut off,not shut down, just switch completely off. The battery meter would say i still had at least 70% each time.
I installed Linux Ubuntu to see if this would solve the problem, however it still does the same thing, when on battery after about 10 minutes it shuts off completely. I have re-installed the latest Bios, tested the capacity of the battery ( windows says it holds 70% of original capacity charge).
What could this be? The laptop ran fine before I upgraded, literally a day after installing Windows 8 it started playing up. One last thing, once it has powered down, if I remove the battery and hold the power button in to release the held charge, and plug the battery back in, it will work for another 10 minutes on the battery! That's why I don't think it's a battery fault. I can keep repeating this until there is no power you see.