That’s an amazing DIY job!
I’m planning to use this:
Zendure 5 Ports USB-C Hub Portable Charger 20000mAh, X6 45W PD&QC 3.0 Power Bank (LED Display, UPS Continuous Power, Low Power Mode) Compatible Macbook, iPhone, Smartwatches, More - Black
https://www.amazon.co.uk/dp/B075Q5VLGK/ref=cm_sw_r_cp_tai_8sA2DbB289E22
It’s a battery with a hub. The Tesla trickle charges the battery, and your phones fast charge off the battery (much faster than if plugged in directly to the Tesla), and a USB key for sentry / dash cam works too. I’m using a raspberry pi for my dash/sentry, so this battery will keep the pi running after the car goes to sleep (not that it matters, but hopefully it will mean the pi doesn’t get uncleanly powered off).