12GB RAM you say. Is it all showing up at its proper sizes in :
About this Mac > ( More Info ) > Memory
All status = "OK" ?
when you run Disk Utility and select That Hard drive by Hadware_name, does the SMART status say "Verified" ??
Are you running into problems with tasks hogging the processors?
Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity
... any over 10 percent?