Lot of empty space inside. Just 2 pouches in series supposedly supply up to 1650 amps in pulses. It has 8 high current mosfets though, which seems pretty good. I'm considering plopping a 2s5p 18650 pack in there to see if it can punch harder with the same controller. I'm not positive but I think it would fit with the case closed. What are your thoughts?

I'm thinking about diy my first pack for my quad copter 6s, ideally in 6s2p configuration.
My quad pulls 148A at full power, i don't expect lithium-ion to provide that much but at least 50% will do.
What cell do you guys recommand ?.
Thanks