In EV conversions I've seen, the fuel gauge is typically repurposed to display battery state of charge, and the tachometer to display power output/regeneration.

In EV conversions I've seen, the fuel gauge is typically repurposed to display battery state of charge, and the tachometer to display power output/regeneration. In modern cars these gauges are all controlled electronically, so it's not so difficult to make them display whatever you like by sending them different signals.