I'm not saying this is the case with you, and fortunately not with me, but if I were unable to afford a new manufacturer-supplied battery to replace a dying one in my laptop, I would rather sell it and buy a cheaper laptop whose battery I could afford. When they are not made to the utmost standards of quality, you could be, again quite literally, putting your life at risk.
Batteries are the one thing in a laptop you shouldn't mess with - I'm fairly sure they're the only component in your computer that is in a constantly controlled risk of overheating, catching fire or quite literally exploding.
