Jm gen 9 m4 upgrade

Hey everyone in a pickle
Need a little advice
New to gel blasters an really into it getting into it with my step son as a bonding thing an well anyway i just brought a jm m4 gen 9 an did a full gearbox upgrade motor is a 8.4v 39000rpm metal gears new plunger metal barrel all that after alot if time spent getting wat I thought was dead rite shimming metal trigger new silver switch an wiring alllll that drama I thought it was rite first run battery smoked when trigger was pulled an only when trigger was pulled now this was the only thing I didn’t replace now I think the new gen 9s have about a 7 volt if I’m rite came with a nylon gear box an stuff so it’s the newer one but I’m just not sure I know the battery is a bit underrated but would it turn the box a little or would the motor being an 8.4 just smoke the battery just wondering if I have a short or a shit wire or … gearbox seems free should have access to a better sized battery tomoro but I wasn’t sure if I should just strip it tonight an check agaaaaain or if an under powered battery wouldnt have the cra k for the heavy spring an metal gears an 8.4 motor thanks sooo
Much for reading that novel new to it all an just not sure if it’s the battery or I should rip it apart an check for a short u would think it would turn a little even underpowered wouldn’t you. ? Or just smoke the battery …