Power Puck without battery holder?

Any voltage divider resistors, filter capacitors?" ... guess Puck does not?

The nRF52 chip has some kind of internal voltage divider for measuring the voltage on VCC - I can't remember exactly sure how it does it internally (you could look it up) but normally there's no problem at all measuring the voltage - there's no external circuitry needed

I surely once mixed +/-

That won't have helped for sure!