But you still have to do regular verifications on this system (probably more than with batteries, because if something goes wrong you would see a 2'000kg disk rolling at more than 100km/h in the middle of town crushing everything in its way).
Why would it? The fact that it rotates ~50,000 times per minute doesn't in the least mean that it will move at all from where it is installed. I've never seen nor heard about SCSI hard disk drives (15,000 RPM) erupting like a chestburster from computer cases and flying around, lol. Rotating whirligig is an obvious example which proves that...
And I think that an internal combustion engine actually requires greater amount of maintenance (given its complexity)