But the contactor cycling remained. Disable remote access in the car, it stops and the car sleeps. Re-enable remote access and the contactors start cycling again. Delete TeslaFi's access token, and the cycling stops and the car sleeps.
I've had TeslaFi disabled for a month now, and the car has been behaving normally. I posted in the support form and got nothing but 5 "me too" responses. I've shut off my renewal PayPal charge and will let it lapse unless they offer some fix.
I didn't want to complicate my original post, but I'm seeing the car occasionally "freak out", disable traction control, ABS, regen, and power brake and steering assist, only to return a few minutes later. I thought I might be chasing a bad ground, ABS wheel speed sensor, etc. At first, my next step was to pull the frunk liner and check/clean the ground studs, but replacing the battery is now an obvious first step.
He was surprised that the battery would die without warning, but confirmed that my other issues (random loss/return of steering/brake assist, regen, traction control and ABS, etc) could be caused by unstable 12V power, possibly causing the gateway to reboot. We'll see what happens.