Most electric cars barely have enough range to get consumers interested, so why are they wasting electricity on electronic in-car gadgets or the ability to for the car to go 100 mph? That's a good question, posted by Franco in Hamilton, Ontario.
In fact, electric cars usually reserve their big battery for the car's drive motor(s) only and still have a traditional 12V lead acid battery that gets involved in running most of the accessories. Cranking up the stereo isn't directly tapping the drive battery in most cases. However, both batteries rely on brake regeneration as a key means of being topped up while you drive, so any juice that is needed to recharge the accessory battery is, in theory, stolen regeneration that could have gone to putting range back into the drive battery.
All of this is relatively minor in terms of impact on range. Things like headlights and climate control take a bigger bite out of an EV's range than do instrument panels and stereos, but we aren't about to dispense with those. As part of my testing of electric cars I always dial up the dashboard readout of projected range and check it with both the headlights and HVAC shut off, and with both on. The projected range reduction is usually in the area of 5 to 7 percent; Meaningful, but not life changing. I don't recall seeing a difference in range when turning on the entertainment/navigation head unit.
As for the ability to drive at extra legal speeds, that only wastes battery charge if you choose to do it. Having a car design that can do 100 mph is largely part and parcel of designing a car that is able to hit normal speeds.
So get out there in your new Tesla Model 3, crank up the stereo, and keep it under 75. But maybe use the sunroof for cooling instead of the A/C.