The 500 mAh is down to 2.6 vdc. Surprisingly, the 150 mAh battery is at 3.7 vdc but I am certain that it goes into a capacitance lockdown when the EPC32C3 begins to draw power and the voltage drops below the power threshold.
I will just continue with my clunky 18650’s. I am learning to build around them a little better these days.