MacBook Pro charger only works sometimes with Macbook?

I have a 2008 Macbook and my charger broke so I bought a Macbook Pro charger and on the box it says it's compatible with my laptop. Except almost every time I go to plug it in, it doesn't work. I have to take out the battery of my laptop and then once it's back in, the charger works. Is there anyway I can fix this or should I take the charger back?

Reset the smc. Apples support site has instructions. If that doesn't work, there's a hardware problem.