I just picked up a PSP slim today and it has OFW 3.90 on it. I would like to put CFW on it. I borrowed my friends PSP slim with CFW 3.71 m33-2 on it and I tried to make a MMS and a Pandora for my psp. So far I am having no luck with it. I tried using the method in the tutorials section but I keep getting an error that says game cannot load when I try to make the battery itself. Am I doing something wrong, or do I need a fat PSP to actually make the battery. Thanks.

Which guide are you using have you using

Have your read here