Wirelessly posted (8800: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0) BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)

Lou, it does seem you've done all the right research.
Yes, the battery could be getting old! But be fore you spend $20-30 on a new battery, try these things.
Remove the battery while the BlackBerry is powered on, replace it and reboot. Allow the battery to drain to about 15% the next three times, and each time, fully charge to 100%.
See if your battery keeps a better charge then.
You said you looked at the FAQs, did you see the link toward the bottom "Maximize your Battery Life"? Some of the tips ouve already done.

Good luck.