Help Replacing 3DS Deluxe Power Grip defective internal battery.

I have a CTA Digital Deluxe Power Grip for Nintendo 3DS (First Gen) in witch the battery has stopped taking a charge. The Grip will still charge the 3DS when the power cable is attached. I have procured an OEM battery to replace the defective one. I just wanted to have an idea of how to install the battery before I opened up the unit. I have been unable to find any information regarding this procedure through Google. Any help would be greatly appreciated. Thank You.