looking for advanced sp acessory

[medwardl]

I'm trying to find a battery pack for the gameboy sp. I saw a sp with a replacement battery but it wasn't a standard one it took the place of the original battery screwing in to the same place as the cover which isn't used with this accessory but it was much thicker and covered the whole back of the sp also lasted much much longer I think it was made by mad catz or pelican but I haven't had any luck finding one or even what it was called to make it easier to locate one anyone know anything about it?