i'm addressing this... firstly, both of my old phones (2 and 4 years) have got blowed up batteries because i leave them on charge constantly, so i don't want to use them for this any more
getting a new one, with a really fat battery, and i should be able to just charge it to 80% and leave it plugged in and turned on with no radios on to an ethernet adapter, or, it looks like the one i'm getting i should be able to root it and set a proper charge limiter so it never charges over 80% so it can stay plugged in (i have an OTG adapter that puts power in at the same time as allowing a device to pull power out)
this device will just sit on my bench behind my pc, emitting no radio waves and all sensors disabled (more certainly, if rooted) and just provide me a bank terminal, end of
then i can use my little baby 2g no data calls and sms only thumb-sized dumbphone for calls and sms, and no longer need to carry around a sensor array just to have phone while out and about
plus, if i do need navigation, i can install that on the new phone (which has a 5000mAh battery) using osmand maps, with all the radios turned off by force and maps all pre-downloaded... i basically know half of this island like the back of my hand anyway so it would be pretty rare, but also nice to have a map that is not gonna break when i look at it with a frown like most phones do, and will stay usable for days on end... so it would be useful if i wanted to go for a hike once this winter cold and damp eases off in may