Gregory's ServerJust to elaborate a bit on that possible use case, let's imagine a relatively low speed vehicle that has a hybrid electro-pneumatic drive train. It's overall air storage capacity isn't huge, but it takes the acclerative power demand off of the electric system which is there to recharge the air tank and augment the engine through different power modes. Overall vehicle weight could be lower, and cost could probably be lower too, given less batteries.
Because the electric system wouldn't be providing all the torque, you could get away with batteries which are energy dense but aren't as power dense.
The vehicle would still be rechargeable like a purely electric system. Range wouldn't probably be fantastic, but could probably be adequate for certain kinds of applications where high torque, start and stop driving, and frequent opportunities to recharge could be possible. A bus or trolley comes to mind.