Tired of losing ECU and radio memory when I replace the car battery myself, I followed the instructions in this video and made my own ODBII memory saver.
- Battery holder GND => pins 4, 5 on OBDII
- Battery holder VCC => diode (+)
- Diode (-) => pin 16 on OBDII
That's it. Stuff the battery holder into the empty part of the shell and reassemble. I didn't even bother to screw the shell together.