Battery Backup Tests, and Using Multiple Unit to Expand Backup Capacity


I ran tests to measure actual Konnected Battery Backup unit capacity Watt-hours, and to measure the effectiveness of using multiple backup battery units to expand capacity.


  • Two battery units were purchased from Konnected. Each battery is specified as “7800mAh”, which is computed by adding the mAh rating of each of the three internal 3.7V Li-Ion cells (2600mAh each).
  • A test load: a 12V LED light string that draws 1.1 amps (13.2 W), measured by DC ammeter.
  • DC-DC Converter 24V -to- 12V (Tobsun EA60-12)
  • Two 120VAC-DC 12V PSUs: The 24W PSU that came with the Konnected board, and an open-frame 12V 36W supply.
  • “Kill-A-Watt” measuring device
  • DC Ammeter
  • DC Voltmeter
  • Time-lapse video camera

Summary Results

Individual Unit Capacity Test - With a 1.1 amp load on the 12V output, the average actual capacity of these fully charged Konnected Battery Backup units is 19.2 Watt-hours each. Ideally, ignoring thermal and transfer losses, a 2600mAh 3.7V cell has a capacity of 9.62 watt-hours. For three cells combined, that is ideally 28.86 watt-hours. Comparing the ideal vs. actual, there is a 67% conversion and transfer efficiency, which is not atypical for low-cost Li-Ion storage systems.

Combined Units Capacity - With a 1.1 amp load on the output of a DC-DC converter, the combined actual capacity of two Konnected Battery Backup units is 38.1 Watt-hours. This test confirms the viability of stacking multiple units to achieve greater capacities.   

Detailed Results and Procedures 

  1. Steps for each trial to measure individual unit capacity 
  2. The battery unit is charged for >12 hours without a load.
  3. A 13.2 watt load (LED string) is added
  4. The 12V charging power source is immediately removed.
  5. A timer is started on the Kill-A-Watt
  6. A time lapse video is captured that includes the timer display, the LED indicators on the battery unit, and the LED string.


Combining Multiple Units to Achieve Greater Capacity

The 12V outputs of two backup units are placed in series, to yield a 24V output. To assure ground isolation, each backup unit is powered/charged by a dedicated AC120V 12V PSU. The inputs of each 120V PSU are connected to Line and Neutral, but are not connected to Ground (e.g. third prong).  



Procedures and Results for the Combined Units Test

  1. Both battery units are charged for >12 hours without a load. 
  2. The outputs are placed in series and the 24V output is verified with a volt-meter.
  3. The unit’s charge inputs are removed, and re-attached, as are the output connectors; while verifying expected voltages for each change. This step is to verify that there were no connection sequence dependencies that might cause the units under test to shutdown due to internal protection circuits.
  4. With no load on the output of the DC-DC converter, the 24V is applied to the DC-DC converter input. The voltage on the unloaded output of the DC-DC converter is verified to be 12V.
  5. As expected, both “battery in-use” LEDs light up when the 24V is applied to the DC-DC converter.
  6. A 13.2 watt load (LED string) is added to the DC-DC 12V output. The string lights up, and voltages are rechecked for accuracy and stability.
  7. The 12V charging power sources are immediately removed.
  8. A timer is started on the Kill-A-Watt
  9. A time lapse video is captured that includes the timer display, the LED indicators on the battery unit, and the LED string.
  10. At 173 minutes, the LED string goes out, and the “battery in-use” LEDs are simultaneously extinguished.
  11. The cases of the battery units, DC-DC converter are checked for hot spots. Nothing excessive is found.
  12. The charge inputs to each of the units are attached, and each blinking red charging LED is lit up as the corresponding power cord is inserted.
  13. The LED string is immediately re-lit when the second charging power cord is attached.
  14. The battery units continue to charge for several hours, while remaining under load.
  15. Case temperatures are rechecked periodically, and no excessive temps are found.
  16. A connection sequence test, step 3, is re-run, and no issues are found.


  • It is completely viable to place battery units in series.
  • The losses incurred by the DC-DC converter are minimal. Combined capacity is very close to N*unit capacity.
  • If the chosen DC-DC converter can handle it, the combined wattage of the load increases by N as well. The limiting factor is the current max of each battery unit.
  • I verified that each unit will charge independently while it’s output is in series.
  • I verified that if ANY one of the outputs drop out, then the series opens up and the discharge of all units stops.

Additional Observations and Concerns 

Unit test: I did not test for the maximum SUSTAINED load while the unit is charging. The supplied power supply for the battery unit is rated at 24W, and the output of the battery unit is also 24W max. Obviously, these two devices together cannot power a 24W sustained load on the battery unit. It is worthwhile to run a test with the 36W PSU to see if the Konnected Battery Backup can sustain a 24W load and simultaneously charge the Li-Ion cells. However, I am hesitant to run any max-load tests on my two battery units as I have plans to use them, and don’t want to have to purchase new units if I fry something.