SCAM SCAM SCAM, and I can't believe both CR & CN have fallen for it.
* First of all, the extra bulk is for a circuit board to control charging, not for any extra battery cell area. The 3700 mAh is going to turn out to be totally fake.
* Second, cells are standard sizes (like 18650 for example), not a gel where the volume of weird extra space would matter. These aren't gel batteries.
* Because of the above, they are only going to fit the SAME SIZE CELLs in them as Canon does, meaning, it's the capacity and quality of the cells that matters.
* Having bought my share of eyebrow raising high capacity batteries and mind bendingly bright lumen rated torches from China, and then tested them, it's all a bit of fun till someone actually believes the marketing numbers....
* Lastly, I would not trust charging a dodgy LiPo battery like these WHILE IN MY CAMERA. The Canon CPS guy would just laugh at you if you tried to make a warranty claim.
SCAM, SCAM, SCAM