Cheapest Power Bank Review (with Schematic)

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. Red blinking LED indicates charging. Steady red light indicates fully charged battery. Blue light indicates a load. When there's about 10% of capacity remaining, the blue LED starts blinking. The power bank is controlled by MP3401A chip and there are just few other components (3 capacitors, 1.5uH inductor and 2 LEDs). The battery space is little bit too short, but you still can insert the battery. The only problem is that there's no fuse in series with the battery. If the chip fails short, the battery will be shorted. In extreme case, this may lead to fire.

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