heltec_t114: enable AUTO_SHUTDOWN_MILLIVOLTS for BLE companions

[yarda]

It should fix #1112, but untested yet (I didn't let my battery to discharge so deep yet :) ).

[ripplebiz]

Please change the base branch to 'dev'

[Xinayder]

3.4V for auto shutdown seems too high. Flat LiPo batteries are safe up until 2.7V, which is the voltage most battery management system chips will cut off.

[yarda]

All board variants in the meshcore repo use 3.3 or 3.4 V for auto shutdown. It maybe good to unify this. I selected the 3.4 V, but I haven't problem with a bit lower voltage. But the value should be safe for most of the batteries. E.g. my battery don't have any BM chip so there is nothing that would cut off the battery. And nearly any battery can be connected to the T114 battery connector. IMHO this is the purpose of the auto shutdown feature, to save the battery from the quick deep discharge. I think this isn't the contest how deep the battery can be discharged and IMHO most of the companion users would prefer durability of the battery (number of cycles) not few more seconds uptime the deep discharge (bellow 3 V) could give them.

[liamcottle]

3.4V for auto shutdown seems too high. Flat LiPo batteries are safe up until 2.7V, which is the voltage most battery management system chips will cut off.

I believe this voltage was chosen, as writing to flash under 3.3v can be unstable and potentially lead to file system corruption, which then requires the user to do a factory reset to resolve.

Safer to turn off early, than too late.

[yarda]

I am fine with both 3.3 V or 3.4 V. I don't think that deeper discharge would give companion users any benefit. Just tell me which voltage to use or what to change in this PR.