Soldering techniques

Hello everyone.

My Pokémon sapphire's soldering points have not been budging, even with proper use of the iron it still would not budge, so I will probably have to have someone repair it for me. This is a good learning lesson I guess, but I would like to do it myself sometime in the future, so in your opinion, do you have any materials or proper equipment I could use to solder my own gameboy batteries?