Here is a manual for you, its not in english but you may need it someday.
http://www.arniesairsoft.co.uk/?filn...sg1/index.html
As for where the battry goes. Copy Paste from a website
"access the battery compartment on the gun, the included adjustment tool must be used to loosen the butt plate. The knob-shaped tool is visible in the above picture. Once the plate is loose, it can be turned so that it's perpendicular to the stock, as in the above picture. Then, a little spring-loaded switch can be pulled back on the battery door, allowing it to be opened. The opened door is also visible in the above picture.
Putting the battery in is pretty straightforward. The PSG-1 can use either a mini, or an AK battery. I didn't have an AK battery on hand, but my 600 mAh mini battery fit perfectly. One interesting thing to note is that the instruction manual's diagram showing how the wires should be inside the stock is actually incorrect. The battery door won't close if you try to wire it like Tokyo Marui shows. Just use common sense, and it'll work fine."