Update: did some testing with a 3w non regulated and a 5w regulated solar panel. Both could run the TTGo by itself, but neither could charge the battery AND keep the TTgo…going.
Mesuring voltage and current drawn while plugged into my car, I discovered that the current drawn when charging a beefy 18650 could reach 0.9amps, which is not unexpected for a Lihium battery as they have a constant voltage/variable current(high at start) charging mode, and a constant (low) current variable voltage stand-by state.
This was far more than either panel could deliver, so the voltage from the panel dropped, the TTGO charger cut power to the board (I think) and all went dark.
Disconecting the panel and rebooting got it up and running again.
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So, I guess that is that. 