Feature request: bluetooth fallback option (from wifi) on power loss

[spfmoby]

Hi

Here is the idea. You have a node on the top of your roof/attic, and it is the "home node", connected to your phone using wifi because the reach is better than Bluetooth. The node is usb powered, with a small battery to allow continuity of service in case of a power loss.

I quickly measured the power draw of my liligo T3S3 connected to my wifi network... il is around 130mAh per hour with very very low activity, screen off...
Powering such a power hungry device on battery is not really feasible. It will eat one large 18650 every day. The idea is to have many days on battery in case of a large crisis (tornado, wildfire...).
So in that case, turning off wifi and falling back to bluetooth could be a very useful idea. But If you don't have AC power, you also probably don't have wifi anymore to manually switch your node back to Bluetooth.

The idea of switching back to Bluetooth in case of wifi failure has been discussed but without any solution.
https://github.com/orgs/meshtastic/discussions/275

An option to switch back to Bluetooth in case of power failure could be a great idea.

Also (if feasible) a good idea could be to add a way to set the maximum voltage of the battery when fully charged, to allow the battery for example to cap its charge around 80% to prevent killing it to fast as it is only used in case of a power failure. It could be useful both on a fixed roof node and a mobile node always on inside a house for example.