A stock Maxx can handle the 7XL on 14 cells ..... the question is just how long!
First of all, your drive shafts will twist after a while, and the yokes will wear out. If you drive hard, the idler gear will fail quick, and the diffs won't stand it for long either.
If you're very gently on the throttle, the driveline may survive for some time, though.
Upgrade as you break stuff is a good idea.
Another thing: 7 cell sid-by-side packs won't fit into the stock chassis, btw.
The sliders are the weakest area of the stock E-Maxx drivetrain. I'm running a 7XL on all stock, except CVDs as I twisted them in a knot on just Titans.