Heng Long Tank: Battery Compart/Options

[Beeg]

I currently only have the HL Sherman and the dimensions I get for the stock battery compartment will fit a battery no larger than 140Lx57Wx27H mm. Is this the standard battery box dimension for all Heng Long tanks?

I like the Admiral Li-ion 7.4v, 3500mAh battery that MotionRC sells but there's a great waste of space in the stock battery box. Without going to LiPo's , what are the options that would fit in the stock compartment for more mAh's and/or more volts? After a quick search NiMH's would provide more mAh's (5000) but if you go for more volts their size pushes out of the box. Doe's anyone make 2s, Li-ion 21700's?

[Beeg]

I'm not sure what the maximum amp draw is on an RC tank but these are a few Li-ion 21700 cells that matched in pairs for a 2s pack I think would make great tank batteries.

Samsung 50T, 5000mAh, discharge 9.8amps - 21700: 70.7 x 21.1

Protected: Orbtronic 21700, 5000mAh, Discharge 9.9amps - 21700 74.8 x 21.49

Sony VTC6A 21700 4000mAh 30A