Top positive review
This Lithium Polymer Battery Bank is a REAL 30,000mAh unit
January 22, 2018
This is a Lithium Polymer battery ... so READ THE MANUAL before using this. This battery does *need* to be fully charged before 1st use. And it does *need* to be periodically (re)charged.
As it happens, after that 1st charge, I discharge then recharge any battery bank 3 times, while I'm measuring the output capacity. (Cycling a battery 3 times -- or "conditioning" the battery -- does nothing for some batteries, but helps to get the most capacity from other batteries.) I conducted those tests using a "J7-t USB Safety Tester". (The best USB tester I had.) And along with that, I used an LED light that provided a pretty constant 250mA load. And yes I know that small a load will provide a *very* favorable result. I used that setup because at only 250mA, the USB tester will not really effect or interfere with the output capacity I am trying to read. For all 3 tests, I got almost exactly 20,000mAh out of the 5V USB port -- which is more than I'd expect for converting the 3.7V battery voltage to the 5V USB output voltage, at not less than 80% efficiency.
***** Battery Capacity vs. USB Capacity *****
Stated capacity for Power Bank: 3.7V battery X 30000mAh = 111Wh (the BATTERY Capacity)
If this unit was 100% efficient: 111Wh ÷ 5.0V USB = 22200mAh (the ideal USB Capacity)
So at only 80% efficiency (22200mAh x 80%) the expected output would be 17760mAh
This is why the "Rule of Thumb" for USB Battery Banks is to expect that the mAh out of the USB Ports will be about 60% of the Battery mAh. (60% of 30000mAh is 18000mAh of USB output.) And again, with my using *very* favorable test conditions, I got considerably more mAh from the USB charging output.