I've bought a 3rd party battery for a Toshiba that worked fine. I bought a 3rd party 3-cell battery for my HP 2133 netbook (because HP wasn't even selling them without the machine) and it gives me a very disappointing run time of about 60 mins (should be more based on reviews of the original battery).

Given all the recent battery recalls, I would be a bit worried about getting a random non-name battery with cells from who-knows-what manufacturer. No one's going to recall those, and you won't know if yours might be affected by a manufacturer problem. Granted, the chances of your laptop going up in flames are probably not higher than crashing on your next airplane ride, but I figured I'd point it out anyway.