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@allObjects
Tried to find a circuit diagram... all I found is some interface in documentation... Reading the details about the 2 wire connector P2 for a solar panel and the 3 wire for battery (LiPo - expected) - especially the 3rd pin on the battery connector P3, which say Charge indicator, and all the suggested applications and available tutorials, I guess it is safe to assume that powering works as expected: a Solar panel up to 12V nominal (without load producing something between 17..18V) and and LiPo battery on the battery connector.
You can verify/this as follows with a 5..9V power source, a 220R resistor, 470R 1/4W+potentiometer (pot) and a Volt - or multi - meter:
A) The volt meter should something below 4 Volts.
b) Measure and write down voltages on Charge indicator pin of battery connector against Ground AND then 3.3V / VCC33 of board (VDD_nRF of P1 or VCC33 of P5). If you see no typical 0 or 3.x Volts value, you may need to connect a 10K..47K..100K resistor across the multi meter probes (Charge indicator is marked as an 'O'(output) type of pin... but it all depends on the board's circuitry whether a load is needed to see actual 'output' - it can be logical output, but physical input, like open-collector/drain).
c) Put volt meter back on battery connector pins.
d) Turning the pot wiper slowly towards the side connected to the + of the power source should show increasing value on the volt meter.
e) When at 4Volts, repeat b) - and you should see same values
f) Put volt meter back on battery connector pins.
e) Turning the pot wiper slowly even more towards the side connected to the + of the power source should show increasing value on the volt meter beyond 4Volts BUT STOP at 5Volts
f) Now repeat b) and you should see at least one of the values having 'flipped', like from 0 to 3.x or 3.x t0 0 volts.
g) Keep the volt meter connected to the Charge indicator and power source the way you notice the flipping of the values.
h) Turn the pot wiper slowly back - towards the side connected to Ground. At one point you see the value flipping again back to about what you measured in step b).
The flipping of the value at the Charge indicator and the voltage at the + at the battery pin tells you when charging of the battery stops or begins - is off or on. The flipping may happen at different voltage depending if the input moves from lower to higher or from higher to lower voltage. The flipping point when going upwards in voltage is called cut-off point, and for a single LiPo battery should be at 4.20 +-0.05 to protect the battery from overcharging (some batteries have one built in, but it is still good to stop charging).
If you have another multi meter, switch it to mA range (0..200...1000) and put it in series with the resistor between pot wiper and + pin of the battery connector. You will then see a change of current flow from neg to positive (value) and vice versa, or from flow (a value) to no flow (0 or practically 0).
Using a digital multi meter may be a little bit tricky... because if the flowing currents pulse, you see values jumping all over the place. Using an analog (old magnetic technology) multi meter balances / middles the values out (but showing lower values). You can 'fake' that balancing / middling out (to a certain extent) by putting a capacitor between the digital multi meter probes and measure thru a resistor and (schottky) diode in series. After a while the capacitor will be charged close enough to the actual peak value of the voltage showing at the measurement point. Taking into account of the measured the forward bias (voltage drop) of the (Schottky) diode, gives enough accuracy (
+-0.5..0.1V) . The reason of taking a Schottky vs. a normal diode is that the Schottky diode has a much lower forward bias vs. a normal (Si) diode:02..0.3V vs 0.6..0.7V and is faster in switching between passing and blocking of current flow and you can measure values thru a Schottky down to about 0.3V.