The RavPower RP-PB060 finally arrived, now operating with the PI. I can confirm charging occurs when driving the Pi. I had first checked the power supply in the powerbank and then the Pi. I turned off the Pi power supply the first time. Oh-oh! So, with the Pi already plugged in, I switched the power supply back on and switched it off again after the Pi had finished booting. It worked — the Pi stayed on through multiple on / off cycles. I'll search it again later to make sure the powerbank holds full charges.