rapid battery drain

I have an older macbook pro (purchased 2006). Works just fine except it seems to be draining the battery rapidly. I thought maybe it was due to an old battery so I got a new one but the new one is doing the exact same thing. And when the battery gets down to 12%, the computer shuts off. The old battery didn't shut off but went to sleep at 0% left. I've tried resetting the SMC but no improvement. Any other thoughts or suggestions? While I certainly would love a new computer, it's not financially possible at this time so trying to make this thing last as long as I can while I save up.