any suggestions for buying a good and cheap laptop batteries?

[Greta2013]

I think it's time to replace my battery. It actually still functions and holds a decent charge but i received a disappointed message from the battery meter/notification area which said: there is a problem and that I should replace it.

Any practical advices for picking up this battery(good, cheap and reputable online places are highly appreciated)? I've found it for around $45 at http://www.batteryselling.com/hp-probook-4510s-battery-8-cell-5200mah-14-8v.html while it is around $30 somewhere else. I just need a brand new, non-refurbished, original hp battery, Amazon, Circuit City and Best Buy are out of my considerations because they aren't carrying this model.

any suggestions are welcome here!!

[David (PassMark)]

If it still works, then I would consider not replacing it.

If it doesn't work, then I would consider at least getting a price from HP for an original replacement part.