as I understand it barrie it originally had a stick battery in the mag so you should be fine putting it back in
What a noob!
There are ribs on the inside of the mag at the gun end which looked like they'd prevent any kind of battery insertion, even a stick battery. However, on closer inspection, one of them has already been filed down.
Also, the "floor plate" just slides off the bottom and a stick battery should go in fine. I'd already taken that plate off for painting as well, how embarassing.
Thanks for the advice all, there should be room for a battery and plenty of bbs too.
If you want it converted properly to mag in stock without the wire hanging monstosity as I did with mine PM me , if you send it up I'll do it as a favour . 
You're a star.
PM sent.
