Full Electric 2004 Jeep Liberty?

Very hard; and very expensive.

The stock electrical system is 12 volt DC, your batteries would also be DC, so you would just have to match the voltage. The batteries, lithium ion would be what $10k at least? The electric motor shouldn't be too bad. The voltage would be very high, and you would have to be very careful not to kill yourself hooking it up! All in all it would probably cost you between $15 to $20k and you'd get about 70 miles to a charge. How much gas can you buy for $15k? The problem is the same as it is for the big car companies. The battery technology just isn't small and powerful enough to be able to give you a 200 to 250 mile range between charges. It's coming, it's just not hear yet.

The real issue is sourcing a $3000 battery pack, and then finding room to put it in the car. Once in, you basically have to hijack an hybrid drivetrain for the electric transmission and compatible engine. Overall, you will spend $15 to $20K having a competent engineer completely rebuild your car, which will be basically useless for weeks, if not months. Then factor in replacing the battery pack every 5 years. It's not a viable solution for the average American - buying a 2 liter four cylinder two seater is far cheaper and leaves a much smaller carbon foot print. That's why hybrids keep falling off the marketplace - long term economic and environmental incompatibility.

Just a thought, but why not hybridize it; use the engine to run the front through the transfer case and electric to the back. Lots of details to work out I'm sure, but should be workable. You should be able to get regulators to drop down the voltage to whatever you want from the EV part. good luck keep experimenting!