Daniel in SD
(beta)
The root cause of the problem is that all idle/vampire drain is drawn from the 12V battery and the battery is periodically recharged by the main battery. The drain is far larger than any other vehicle (ICE or EV) so it kills even the more expensive AGM batteries quickly (the original Model S had standard lead acid batteries and they wore out super quick!). It's not a function of mileage but time/cycles. I bet if you were to drive the car 24/7 the 12V battery would last a decade because it would never be discharged.The problem is the only way to get "automotive 12V" out of the main pack is to use a DC/DC converter, or tap 4 bricks. If you use a DC/DC converter, that's fine, but how do you get it to stop working when there's a problem? Does the car have to get another pyro disconnect?
And if you tap 4 bricks, you'll get 12-16V, which is consistent with automotive 12V, but you'll cause an imbalance in the battery pack, unless you design some complicated mechanism to change which 4 bricks you're connected to in an automated manner.
I'm sure all the Model 3's with failing batteries are causing someone at HQ to wonder what would be better. If it was cheaper, I would expect Tesla to start putting LiFePO4 12v batteries in the cars.
But the truth is, 12V needs to go. Sure, there's lots of stuff that works with it already. But moving to 24V or 48V would allow smaller conductors and/or reduced power losses. It would require Tesla to source automotive equipment that worked on 24/48V. But that's the future.
The question is why don't they keep the DC/DC on all the time? I have no idea.
Completely unrelated but 48V has been the future for decades. I've become skeptical it will ever happen.