PSP charge grip

my friend want to buy this grip to compliment his PSP which he said will add confort and a firm grip (http://www.sourcingmap.com/rechargeable-grip-for-sony-psp-black-p-864.html)

I tried to convice him to buy a spare battery instead, cause i know some issues

Give me your expertise so i can make sure

Thanks

i have heard that in some case the battery dead soon...