I don't know much about cars or helicopters, so I have an honest question: why would the maintenance for an electric helicopter be less expensive than the maintenance for an electric car?
The big money saver would be the engines. Most big helicopters run on turbines and they are not cheap. And they have a limited lifetime before you're legally required to overhaul or replace them. For the engines on business jets that a friend of mine used to charter pilot, that number was between $500 and $1500 per hour.
If you built electric motors for a chopper you could theoretically design so that it had 8 motor any one or two or three of which could fail and still fly. Make several different independent battery packs and you enjoy more robustness. If you engineered it right you could make the case to the FAA that the helicopter doesn't need any expensive preventative maintenance on the motors or batteries, just on the drivetrain. Which would save a lot of money.
EDIT: "most helicopters" to "most big helicopters"
Sorry, I should have been more clear - I meant the maintinence would be inexpensive compared to a gasoline piston helicopter. Given the requirement for safety in aviation, piston engines have to be inspected (and rebuilt, at a cost of ~$50k) every ~2000 hours the aircraft is flown. This cost essentially goes away with an electric engine, partially because they last 10x as long, and partially because they cost significantly less than a piston engine.
My inclination is more expensive. You'd probably have to deal with more vibration causing more mechanical wear, and tolerances would have to be might tighter since the stakes would be higher. On the plus side you'd have less road-wear related issues, but many (probably most) car owners are able to neglect those things for years.
Nobody literally goes over a pre-drive checklist before driving down to the grocery store.
If you built electric motors for a chopper you could theoretically design so that it had 8 motor any one or two or three of which could fail and still fly. Make several different independent battery packs and you enjoy more robustness. If you engineered it right you could make the case to the FAA that the helicopter doesn't need any expensive preventative maintenance on the motors or batteries, just on the drivetrain. Which would save a lot of money.
EDIT: "most helicopters" to "most big helicopters"