Solar cell results: While the solar cell generated enough voltage to trick the Duracell into thinking it was being charged, switching on the charge LEDs and output, there wasn't enough current to stay ahead of the game. Adding more cells would help, but there will still be boundaries at dusk or cloudy days where the Duracell will be switched on only to lose ground.

Raspberry Pi: That worked well. A RPI 1 B+ with wi-fi running as an open access website can be run for at least two hours. The RPI Zero would be ideal for that. (Tip: Add a clock module if you want to the logs to make sense.) The built-in micro-USB connector makes it neat and tidy.

Where now: The supply of these power packs seems to have dried up. I doubt I'll see any more. I sacrificed three of them for the batteries, and I'm keeping two un-hacked for phone and Pi use.

Meanwhile, more power packs are sliding down the clearance pricing. At the Dollar Store the current $3 special is a "Power Bank" unit of similar capacity, but simpler design without the inductive charging feature. I'll dissect one soon. (Maybe the guts will fit an Altoids tin.)