A few years ago, the neighbor's tree blew into the wires and took out our whole neighborhood's power for six full days. After a while, charging the phones and other devices in the car was running down the car battery. I wished at that time I had a sensible way to easily charge off of my 3S airplane batteries.
When ESCs burn out, it is almost on the motor output side; the BEC 5 Volt circuitry is almost always still functional. Here is how I made a free RC LiPo battery to ESC to USB-A charger for emergencies.

Here is the standard layout for the USB-A female socket, viewed as you look into it. You have a bunch of these in that box full of no-longer-used cables and wall warts. Just carefully get the socket out and clean it up so you can solder to the outer two connector points ( the two inner ones are data.)
The red "servo" wire coming out of the ESC solders to the +5 V pin. The black wire goes to the -5 V pin. The yellow or white signal wire just gets cut off. Make sure you don't reverse the polarity or you may damage devices you are trying to charge. Maybe use a voltmeter if you have one.
Make sure you don't reverse the polarity or you may damage device you are trying to charge.
The finished charger after cleanup, shrink tubing, and labeling: Try squirting "Granny glue" into the shrink wrap around the USB socket for a nice strong result. I labeled mine so I can figure out what it is later.
This will easily charge any device that uses 5 V USB charging. Now you just have to remember where you put it!