For reference from the other Q:
It sounds like you may have multiple problems here:
* First lets reset the SMC logic so the level of charge the battery has is correct [http://support.apple.com/kb/HT3964|Intel-based Macs: Resetting the System Management Controller (SMC)].
* I would download this little gem to better monitor the battery [http://www.coconut-flavour.com/coconutbattery/|coconutBattery 2.8].
* I would also download a good temp & fan monitoring app like [http://www.tunabellysoftware.com/tgpro/|Temperature Gauge Pro]. While there are others this one is the best one I have found.
Now with the better diagnostic software running what is it telling you? Is the battery worn out? Is the charging circuit having problems? Is the temp running high and the fans not working?
Given the age of your system you may need to clean & reapply thermal paste on the CPU & GPU chips heat sink and clean out the dust buildup thats in the system. But for now lets see what the new tools are telling us.
Snap a few screen captures and post them here so we can see whats up.