Do a search... there's a thread on how to figure out your battery capacity. You didn't say what size your PowerBook is... but the 15" max capacity is 4600. My new battery reads at 4417, which is fine for me.
Also, my new good battery lasts over 3 hours easily with all the extras on... bluetooth, wireless, display on brightest, etc. Conserving battery life doesn't matter if you're only getting an hour out of it. You'll probably just need to get a new one.