Backup Battery

With the recent discussion about backup batteries, here's an out of the box thought, I have a number of Milwaukee M12 battery tools and continue to be amazed at the battery standby life. Some of the tools do not get used for months and they show fully charged and ready to go when needed.
I recently ran across a M12 battery dock intended for Robotic, PowerWheels and other child toys. Link here: https://www.amazon.com/Battery-adapter-Milwaukee-connector-robotic/dp/B08LCDJG5M
This battery adapter could be mounted in an out of the way, accessible spot on the aircraft and only used to power the E buss. With no parasitic drain the M12 battery would last for months and could be swapped for a fresh battery from the M12 charger. With no charging function taking place on the aircraft, the wiring would be simple and it removes the worry about overcharging, fire and the like.

An extra 12 volt at 6 Ah may come in handy when the lights go out.

Popcorn ready

Have you tested the output voltage of one of those batteries to see what the voltage is under load? I too have several Milwaukee M12 powered tools with several M12 batteries, but never thought of using them in my airplane. I have a Milwaukee M12 charger and power source device and wonder if that could be used to power a mini endurance bus when you have a failure of your onboard charging system.

https://www.amazon.com/Milwaukee-48591201-Charger-Portable-Source/dp/B07849X7BF