Hmm, I wonder if I could experiment with the serial arrangement. From the tutorial:
[The regulated load output] pin will provide a regulated output when the input voltage is below the over voltage protection threshold and above the regulation voltage. It will never be higher than 4.4V (but it may dip down to 3V or whatever the LiPo battery voltage is at, if USB/DC [isn’t] plugged in)
That said, elsewhere it says:
DC/USB/Solar is prioritized over battery power when available, to keep the battery from cycling
That would mean that during the day, current measurements would be meaningless, as they might represent the output of the panel!
That does give me an idea though - perhaps I could use a light sensor to determine whether the panel is doing anything. When it has gone dark for more than a few minutes, it can be assumed that the fuel gauge is measuring the battery 🤔