RE: Extra 330L-EP Extreme 3D RC Acrobatic Plane ARF
That's a pretty big plane to go electric.
It's doable, but you'll need the equivalent of a 1.20 4C engine to do it or a .75+ 2 stroker.
Given 2.4hp or better...
745 watts per HP x 2.4 HP = 1790 watts
Assuming 22v
1790 w / 22 v = 81 Amps
So you would need a motor capable of 1790 watts @ 22v and a battery pack capable of about 100A or better.
You can use multiple packs to get there, but at this level I'd just go with a small gasoline engine instead.
You could also use two 14.8v packs @ 29.6volts and 60A total draw to get the same, which would dovetail with the packs used on the Extra.
But you'll also need a high voltage (HV) ESC, separate BEC, etc.
Your biggest problem will be changing out the battery packs.
There are no provisions for this in the Ultimate 1.20 and there is no easy way to cut out a battery hatch, especially since you must leave the fuselage structurally sound to support the carbanes.