[Don Plumley]

Here's a plug for the OEM battery from Apple: Make an appointment at the genius bar. The tech will run diagnostics on the computer to confirm without a doubt that it is the battery. Some batteries have recalls and might be replaced for free (if the computer is very old, probably not). The battery then has a warranty. They will also properly dispose of the old battery (you can't toss it in the trash at home).

My time is well worth the extra bill to not have to buy a battery online that may or may not work, fit, etc. YMMV.