When my MBP (OSX 10.4.11) is running on battery supply it turns off without warning when approximately half the battery is depleted. I have no idea how to troubleshoot this problem. Also the 1 year complimentary warranty expired and I was considering purchasing AppleCare.

Nobody knows?

I think Apple has a battery update download on their support website, only idea I have. That and Google.

Good luck.

I have all the latest updates

How about google?
http://discussions.apple.com/thread.jspa?m...56&tstart=0

Maybe you need a new battery.

I downloaded Coconut Battery and I figured out that I do indeed need a new battery:

Battery Capacity:

Current: 3608 mAh

Original: 5500 mAh

...Or 65%

I noticed that whenever my battery is fully charged, it never exceeds 95% even after I recalibrate the battery (which I did every month or two starting from the day I got it)