Bought a couple of cheap power banks off EBay before xmas for presents. Kept myself 2 of them.
They have a solar panel, 2 LED bulb torch and claim to be waterproof.
Now for the LOL part. The description claims "300000mAh", aka 300Ah. A lead acid battery would need to be the size of a suitcase to deliver that much capacity. The product blurb tries to bullshit about this being a derived value based on the solar panel working at the same time or some rubbish.
https://www.ebay.co.uk/itm/Waterproof-300000mAh-Solar-Power-Bank-2USB-Battery-Portable-Charger-for-Phone-UK/152214561530?hash=item2370b1e2fa:m:mz_Pr8pZEPBulwPTvfEnxfwI tested it multiple times from it rejecting anymore charge to powering off 5 times with a 5 minute rest in between, to get it fully discharged. 2000mAh. Confirmed in discharge and charge (using the same analyser admittedly).
However now I have taken it apart I can see it has a single LiPo pouch cell that it very likely to be a 2200mAh cell. It's unlaballed.
The solar panel is a nice idea, though they of course claim it's theoretical output of 200mA.
Now it's not all that bad. I tested it in afternoon winter sunlight today, indoors with a window in the way by running the 2 LEDs from the torch unit on it.
Open circuit it was producing 5.4V
Running the LEDs it was producing 2.6V and 25mA.
I could gather in direct summer sunlight, directly angled to the sun it could produce 50mA, 100mA tops, but I'm guessing here. 200mA, I doubt it. 200mA @ 5V would make it a 1W panel. It's only 2" and 4" in size.
Now for another LOL. While in the unit, should the solar panel get enough light the unit displays a number of LEDs, a green "solar" light and then a chaser lighting up another 5 blue charge LEDs.
You can see the problem. While running all those LEDs + the Micro to run them there is no power left to charge the battery. Over Christmas I drained it and left it in the window for a full week and tested how many more mAh I got out of it after that and achieved 12mAh before it power off.
My brother claims he left one in the window for the whole summer and it fully charged. I'm not convinced. I think he forgot it was charged when it left it there.
Well, in the end I have a nice board with 2 torch LEDs on it, a LiPo pouch cell with a power bank board hanging off it and a 0.5W solar panel which I'm not sure what I can do with. 20mA is enough to power an arduino, but not at 2.6V. Better sunlight and outdoors it might stand a chance of running an Arduino and a few very dim LEDs.
Can I get it to charge the LiPo cell using a TP4056 with it's LEDs removed I wonder.