USB battery box EPCTEK 20000mAh

More than one power bank is called EPCTEK 20000mAh


The box has a unknown number of batteries and two usb outputs.
The specifications are: I bought the box from Ebay seller: eoutlet_uk

How does it look


The power bank is delivered in a white cardboard box without any markings.


It contains the power bank, a usb cable and a manual.


The two output connectors, the micro usb input connector and a white led is placed in one end of the box.


On top of the box is the 4 leds to show charge status and a button to turn on the status leds on and activate the white led.
A single press will activate the status leds and turn the output on, a double press will turn led white led on or off. The double press does not turn the status leds on or activate output.


The bottom has some labeling about capacity and current.


I do not know if the box contains 18650 cells or a Lithium polymer pack, but the above picture gives an idea about size and how many 18650 could be fitted.


I could not open the box, i.e. there is no measurements directly from the battery, only from the input and output connectors.


The first test is a load sweep to get an idea about the performance. The two outputs looks identical and can both deliver 2A, the overload protection kicks in at 2.4A.


The output looks fine at 0.5A with about 8000mAh capacity, this is way to low for a 20000mAh box.
Note: Specifications always list battery capacity, output capacity will about 60% compared to that, due to the voltage difference between battery (3.7 volt) and output.


The output also look acceptable at 2A, but voltage is on the low side.


Looking on the output with an oscillioscope show little noise, it has 24mV rms noise and 160mVpp noise at 1.6A.


At 0.5A the noise is down to 7mV rms and 70mVpp.


The specifications says the box need 1A when charging, as can be seen on the curve it can use up to 1.6A and the battery capacity looks to be about 11000mAh. The charge curve looks like CC/CV. The real capacity is about 11000mAh.
It takes about 9.5 hours to fully charge the power bank.


Adding some series resistance, equivalent to a long cable or a weak charger reduce the charge rate significantly and increases the charge time to nearly 16 hours.


Except for the wrongly specified capacity this box looks fairly good. It is a bit silly that the 1A output is coded for 2A Apple and the 2A output is coded for 1A DCP. Remembering to charge Apple equipment in 1A and other stuff in 2A can be used as a workaround.

The box is good, if the lower capacity is acceptable.


Read more about how I test USB power supplies and chargers