T114 solar charging issue

[n0qbh]

I was having trouble getting a 3.7v LiPo battery to charge on a solar powered Meshtastic node.
When I replaced the 5W 5v solar panel with an adjustable power supply I discovered the charge rate dropped to almost zero at 5.0 volts input.
The orange LED would light but no useful charging would happen until I raised the voltage to 5.1 volts.
My two RAK nodes don't appear to have this behavior.