If you're into modding, then better read this DIY guide written by Echigoya guns... "This guide is how to fit a battery inside the Magpul PRS Buttstock. In order to do this you must have the proper equipment, and we advise that you do this at your own risk. Also make sure that your receiver is strong enough to take load of the stock and hard enough take threading tools. I strongly won’t recommend using Tokyo Marui receivers, their metal is only diecast and it is not rigid enough to handle and keep the buttstock in place."

Read the full DIY story here. Make sure you have all the necessary tools and materials to do this.