This somewhat exaggerated power bank has one of the simplest circuit boards I’ve seen yet. Just 5 components and the connectors.
To keep the chip’s pin count low it uses the arrangement of the charge and output USB sockets in parallel. That means that it has to dip the voltage briefly every couple of seconds to check if a charger has been connected.

Quite well constructed with LG cells, an unusual control PCB with a few tricky to trace components and a thermistor for battery temperature monitoring. Notable features are the decent control chip they seem to have used and the matching beefy inductor.

External cell capacity test is a respectable 6400mAh. (3200mAh per cell)

Test and teardown of a PowerBank designed for two 18650 Li-Ion batteries. The sellers on Ebay call it “DIY” for a simple reason – it comes with no cells and you have to put your own 18650 Li-Ion cells into it.

Most of Poundland’s power banks in this style come completely discharged due to the higher than usual quiescent current of the circuitry. I wanted to know if that was a serious issue or not.

I was trying to simulate what happens, if the chip goes short circuit inside a power bank with a 18650 Li-Ion cell. As usually, my experiment went wrong. You can enjoy lots of smoke and fire. Never try to do this experiment, it is very dangerous.

“… sophisticated dead short circuit simulator, or a blob of solder”

Test and teardown of the cheapest power bank ever – the 80 cent (incl. shipping) power bank from Ebay. Of course, you have to insert your own 3.7V Li-Ion 18650 cell into it :). What did you expect for 80 cents :)? It works well for loads up to 1A. At 1A the output voltage is 4.94V. At 1.1A the voltage drops to 4.56V and at 1.25A it shuts down. It charges the battery to about 4.2V and discharges it down to 3.1V. While charging, the power bank draws 0.78A from a 5V supply.

A look inside the slightly notorious (recalled) EE Power Bar and some analysis and tests to see if it is as dangerous as the media made out.

In brief, a UK based mobile phone service provider made these handy power banks available with their contracts, with the novel idea that if you were caught short for power you could pop into their nearest shop and exchange your flat Power Bar for a freshly recharged one.
Then there were some incidents where the Power Bars caught fire, with one incident resulting in a picture of a burned hand

A look inside a few different 18650 style USB power banks, including a test of their quiescent current in standby and their upper and lower charge/discharge cutoff points.

Scarily tight aluminium USB power bank.
https://www.youtube.com/watch?v=lXuevtvchQQ

It’s VERY tight inside to say the least. The battery and the thin wire that runs up its side are a tight friction fit in the tube, and the length is absolutely on the limit for the 18650 style lithium cell and the PCB. It was quite scary to take apart and reassemble

While doing a discharge test on a small USB power bank, I discovered that even though the booster circuit cuts out when the lithium cell’s voltage drops to about 3V, the load can still draw current through the boost inductor and diode. As such, if you leave a load connected to a USB power bank that has run low, it may still drain the lithium cell down below it’s safe discharge level and damage the cell.
So the moral of the story is to avoid leaving loads connected to USB power banks for long periods of time.