https://forum.pjrc.com/index.php?threads/does-vbat-accept-4-3v.45290/
Does VBAT accept 4.3V? | Teensy Forum
The real-time-clock battery port is intended to connect to a CR2032 or similar battery. There exists the LiCR2032 cell, which is a small lithium-ion...
vbatacceptteensyforum
https://www.utasker.com/forum/index.php?topic=2017.0
VBAT Detection
vbatdetection