I've purchased a FireFox 11.1V 1600mAh Mini Li-Po Battery measuring at 102mm×34mm×16mm (L×W×H), I know that the dimensions are almost if not identical to a Ni-Cd or Ni-MH mini battery, but believe me, Li-Po's that are this size will not fit in a TM SIG SG 552 AEG or Clone. They have straight and sharp corners that make it impossible to fit in the handguard even with the battery tray removed.
I recently just purchased a SOCOM Gear 11.1V 1000mAh Nunchuck Li-Po Battery measuring at 100mm×18mm (L×Diameter) on one pack and 50mm×18mm on the other pack and it fits perfectly in my TM SIG SG 552 with the battery tray removed. The Li-Po pack sits snugly on top of the inner barrel inside the handguard. Same goes with the SOCOM Gear 7.4V 1000mAh Short Stick Li-Po Battery.
So if you own a TM SIG SG 552 or a clone and are looking for a Li-Po battery, your best bet is to go with the SOCOM Gear batteries that I mentioned above. Just a little info that I wanted to share with SIG SG 552 owners.
