No need for a new controller, unless a new battery does not fix it.
EV globals are 24v or 36v, and brushed motors. In some ways, your easiest thing to do is keep the lead. Open the original battery pack, and then replace the lead with new cells. Easy to do, or if you don't feel up to it, take it to a Batteries Plus, and they will put new lead in the box. Then you can also still use the original onboard charger.
That will work fine if your use pattern is not a real long ride, like 6 mile trips or so.
You can replace the battery with any 24v or 36v ( whichever you have) lithium battery for bikes, but typically it wont fit exactly in the original pack. So you have to get into the bikes wiring to connect some new wire to the controller, and a plug that will reach your battery carrying location. Usually, that's on a rear rack top for an EVG. Charger will be what comes with the bike, but no longer onboard.
If you want to do that, you have to get into the bikes wiring. Down on the bottom of the frame, there is the two contacts that the battery box contacts connect on. You'd get into there, and attach new wire to the wires leading to those two contacts. Red positive, black negative. The new wire would then go to your new battery on the rack.