This sounds like complete nonsense but if someone else can confirm, I'll be willing to try, once my battery becomes useless

It indeed does work with a lot of cell phone batteries. Many ppl have already done this with different cell phone batteries

I even remember some people doing this with normal AA batteries. I think there was even an article her on QJ, but I don't want to search for it.

this same thing will fit a slim battery for anyone wondering. i actually had a spare of the higher capacity version BL-6C. i did i last night. for some reason i couldnt get it to work though. i wired the positive and negative of the battery to what i though was correct but then every time i put it in the psp and tried t turn it on, the board for the battery would instantly get really hot, so i though maybe i switched the positive and negative on the board, so i swapped them and tried again only then it just didnt work at all. when i had it in the psp while plugged in, it would give me the orange charging light but i wasnt really doin anything. if i turned i on it would only run from external power and didnt display any battery information. i dont know what could be going on. It's more than likely just the slim battery board not taking the battery or something. i know it doesn't make any sense, but its the best guess i got.

it was with 3xAAA batteries. you can actually buy those batteries now and simply put AAA's in them.