I have a friend who has two PSPs, a phat one and a slim one. He uses the phat one for homebrew as the UMD drive does not function and the slim one for actual UMD gaming.
I am not sure what firmware he is using on the phat PSP however let us assume it is an official Sony one.
I have heard something about a battery trick that requires a phat PSP and something about a modified memory stick.
I am wondering if there was a guide for a complete noob that tells the steps of actually creating said battery and memory stick and goes all the way through the steps of actually getting the custom firmware on a slim PSP.