I'll guess 347fps w/ 0.20g bbs....what do we get if we win?
If it's a 9.6v 1500mah mini made up of 2/3A cells, the battery should be able to pull a M120 with a TM EG1000, System Magnum, Guarder Infinite Torque Up, G&P M120 High Speed. It should also work with a
new stock CA motor (but I don't really trust them for longevity...). Those are the only motors I've used in my own rifles with that battery/spring combo. Obviously the Magnum motor rocks. Don't expect the battery to last all day if you shoot a fair bit.
I don't know what the gear ratio is in that Systema complete mechbox...and sorry, I'm too lazy to look it up.
Why would you put a mini battery in a crane stock? Even the G&P crane takes cells larger than 2/3A and many take large cells (which can maintain a good dumping of power and tend to last all day and then some, at least for me).
Best of luck...let me know if I win the FPS guessing game (and BOO to those who guessed a huge range...

).