USB battery box 2x18650



I found this box on ebay, specifications is something like:

• This is the newest version, can be used directly and don’t need press any activate button.
• USB Output: DC5V 1.5A
• mini USB Input: DC 5V 1.5A
• Color: Black
• This box can charge ONE or TWO piece of 18650 battery and other Square polymer lithium battery( Battery not included)
• Can charge most cell phones as well as iPhone, IPOD, IPAD and other Apple products;
• Has reverse connection protection, has over charge and over discharge protection;
• Box size: 107 x 43 x 25mm

The box is an update of this unit.



How does it look



The box arrived in a envelope without any accessories.



The box is fairly compact. It is controlled with a switch on top of the box. There is four blue leds around the switch.
A press on the switch will turn the output on, a double click will turn the led on or off, there is no special "battery disconnected" state.



This hole is not used on this version of the box.



All connections are placed in the same end, mini usb for charging input and normal usb for output. There is also a led for flashlight usage and a led showing when the output is on.





To replace the batteries, slide the bottom off the box. The batteries can be up to 69.7 mm.





Measurements

• The output will first turn off when the load is removed.
• When output is off the battery drain is below 35uA (This is more than 20 years with a full load of 3100mAh batteries).
• The USB output is coded as Apple 2.1A.
• When charge input is supplied with 5 volt, the output has a lower output voltage, i.e. not useable as charge output.
• A double click on the switch will turn the white led on or off.
• A single click with the switch will show battery status on the leds.
• When battery voltage drops below about 3.22 volt a single blue led will flash when showing battery status.
• There is hysteresis on the battery status indicator, i.e. the led does not turn on and off at the same voltage.
• 4 led off at 4.02 volt, 3 led off at 3.69 volt, 2 led off at 3.55 volt
• The red led is on when output is on or when charging the box.
• When charging a blue led is flashing behind the button.
• When finished charging all the blue leds will be on.

I did the load sweep up to 2A, the box did not turn off its output, but keep the voltage close to 5 volt all the way.



With a 1.4A load the box can keep the voltage up for about 2 hours.



Reducing the load to 0.5A, extends the runtime to nearly 7 hours and the box has a very good efficiency.










With 1.4A load the noise is about 180 mV



Reducing the load to 0.5A will reduce the noise to 60mV




Charging is with constant current and measuring the voltage with the current turned off. Because the CV part is missing, this will give a fairly fast charge, but to fill the batteries completely the charger needs to go above the maximum voltage for the batteries.
It works, but I will recommend charging the batteries in an external charger.







With all the test batteries the charge voltage is above 4.3 volt, this is not very good.



Conclusion

The box works is good for supplying current and is easy to use, but the charging circuit for the batteries is not very good.
The hysteresis on the battery indicator leds, makes it better at indicating battery voltage.



Notes

Read more about how I test USB power supplies and chargers