I am considering the same thing. I would approach it by fitting a second battery pack in parallel, and fitting a plug-in charger.I am considering buying an old hybrid and converting it to all EV. I was wondering about how the conversion would work with the existing computer. Would it interfere?
Keep the ICE generator, until those bits are sorted out. The generator should only run, when the battery can't keep up with the power demand. Drive the car for a few months to see how it performs.
Experiment, and decide how to proceed. Can you fiure out how to unpatch the ICE generator, and still drive? How much electric range do you get? How many kW of capacity will you need? More of the same batteries, or something with more energy density?
Hybrids already drive on electric power. Ultimately, removing an engine, upgrading the batteries, and fitting a charging system sounds a lot easier than a full ICE to electric conversion.