ZE4700 Battery Problems

So last week my neighbor stopped by, he asked me if I could help him set his desktop PC back up. He had new carpet installed so it was disconnected. Anyway I went over and put everything back together, checked to make sure printer worked, etc. On my out he gave me an old laptop of his as a thank you, told me it was really slow but maybe I could do something with it.

I checked it out and it's a HP ZE4700, from 2004. It looks like it's hardly been used and there was a fresh install of XP on it. I immediately figured out why it was so slow: there was only 256MB of RAM in it. Also, there was no wireless card in it.

So I ordered 1GB of RAM and an $18 wireless card from NewEgg, now that I have everything installed it's fairly snappy - good enough for web surfing or watching a movie or whatever.

The problem now is the battery. After reading this thread I think the battery is just dead:

http://forum.notebookreview.com/showthread.php?t=434945

Been looking at new batteries for this guy, it's the f4809a/f4812a battery. Looked at this unit from Amazon:

http://www.amazon.com/Battery-Compaq-4098a-f4809-319411-001n/dp/B001QWWYV4/ref=pd_cp_e_1

anyone have experience with the cheaper replacement batteries? You can get the HP battery but those run about $100. I'd like to get this laptop in good working order but I'm not so sure it's worth spending much money on.