psp phat trade with slim?

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ok i have a psp slim gray. the battery cover wont stay on completely so it can just fall offf kina easy. i want to trade my frend for his phat which is in like 85% good condition. what else shuld i give him like money to make up for the battery cover. oh and the little hole that the clip on the battery cover goes to is boroken i glued it back on but not that even.