Amazon can afford solar panels and batteries, so their electricity unit cost is going to be extremely low. Even when they need to pull from the grid, they can do it overnight when prices are lowest.
EVs cost a lot less than fossils to maintain. No engine oil or filters, no exhaust system, no spark plugs, no fuel pump or injectors, no water pump, no variable gearbox (on most), even the brakes hardly get used thanks to regen. For commercial operators with fleets of vehicles, those savings add up fast. You can bet that the vehicles Amazon uses are very simple, and the only complexities are things they would fit to a fossil like telematics so they can see where they are and how they are driving.
As for consumer EVs, there are loads of simple ones. The Nissan Leaf is a good example, one of the first and a very straightforward machine. It's easy to replace or upgrade the batteries, the BMS handles it without any reprogramming. It all works fine without the infotainment unit even being installed, and the base models didn't have telematics.