TESTING: PowerCore Essential 20000 PD

So there was this:

And I bought this:

And @professor provided a testing plan. So this is really his results. I was just the errand boy, the technician who ran the tests. And supposedly the results are interesting. So here they are.

iPad Pro 11 (2018). Battery capacity of 29.45 Wh.
Anker PowerCore Essential 20000 PD. Battery capacity of 72Wh.
Klein meter shown above.

15V Test:

  • Depleted my iPad to 0% (shut down on its own).
  • Used the PowerCore to recharge the iPad (USB-C PD at 15V).
  • Depleted my iPad to 0% again.
  • Used the PowerCore to recharge the iPad (USB-C PD at 15V).

5V Test:

  • Depleted my iPad to 3%.
  • Used the PowerCore to recharge the iPad (USB-A at 5V).
  • Repeat until PowerCore was depleted.

15V Result:

  • The meter measured 67.54 Wh from the battery (72 Wh) = 93.8% PowerCore efficiency.
  • The iPad was recharged 1.83 times. (29.45 x 1.83) / 67.54 = 79.8% iPad battery efficiency.

5V Result:

  • The meter measured 69.49 Wh from the battery (72 Wh) = 96.5% PowerCore efficiency.
  • The iPad was recharged 1.96 times. (29.45 x 1.96) / 69.49 = 83.1% iPad battery efficiency.


  • I had several cables to choose from. @professor provided guidance in choosing the most efficient cable to run these tests.
  • For both 15V and 5V tests, the iPad charged rapidly until around the 80% mark, then it gradually slowed down (same voltage but lower amps) as the iPad approached 100%.
  • The Klein meter is not that great. I had to set up a webcam to capture what was going on: when the test ended, the total Wh used, etc. I usually unplugged 30-90 minutes past the end of test. After iPad reached 100%, <0.05 Wh was consumed for trickle charging for each test run.
  • For the 5V test, I had to start the iPad at 3%. When it was 0%, the iPad would not recharge. Maybe it was because of the meter in the middle? Not sure, but at 0% and even at 1%, the iPad would not recharge. This is why I started at 3%.

If you have technical questions, then @professor can answer them.
If you have questions about the setup, then we may both be able to answer them.


Good work!

This was a test of some hypothesis:

  • how efficient is Anker Powercore at converting the energy of the cells to USB voltage output port
  • how efficient are USB cables at different lengths and voltages
  • how efficient is a device at voltage conversion overall.


  • Anker Powercore 20000 PD is excellent, exceptionally efficient. We saw 96.5% efficiency at 5V and 93.8% at 15V.
  • There is a slight advantage for 5V for the Powercore (but see other points to balance)
  • We measured the resistance of the cable. For the 15V test it was a C-C, 5V was A-C, and these lost 0.27% and 2.75% efficiency respectively. This is because lower voltages forced the current to be higher and energy lost in cable is to the square of current x resistance. So while the Powercore was a little more efficient at 5V, some more energy got lost in the cable to narrow the results.
  • The iPad was the villain here. It was 79.8 efficient at 15V and 83.1% efficient at 5V.
  • When you combined the losses higher in cable, and in the Powercore, and the iPad, combined these led to a net overall efficiency of 75% at 15V and 80% at 5V.
  • Overall net therefore, use of 5V is more efficient combined, even though the cable lost more energy, you got more out of the Powercore and in the iPad
  • Conclusion: if you have a smaller Powercore where you want to get the most, use the shorter A-C cable. If you have a larger Powercore given the recharge times overall are significant faster then on balance might as well use the C-C cable.

Cool analysis. Thanks for doing this testing!

1 Like

So this implies 75% total efficiency for 15V? That’s pretty good!


Great tests and interesting results. Thanks for doing this

75% for 15V, 80% for 5V, having already tested and not used the worst cables. Most of the losses in the iPad. Which makes sense as the recharging is the most loss. My intention is to edit the 2nd post I inserted with more math on the losses so we can point to it when the next person complains mAh is not as advertised.

This is a good example of where the 2/3rds rule comes from. 75% is not that far off 67% which is the basis of how I calculate the assumed phone recharges from a mAh number.

96.5% efficiency from Anker. That is… well… very impressive… then 0.4% from the cable (I have more data) and most of the loss is the device (in this case iPad).

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Great work!!! :ok_hand:

Good made test.
This is what we all like to see.
Helps others a lot.
Thank you and enjoy Sunday

Great work @onstar
That’s interesting as I have that PowerCore and iPad.

Nice collaboration between @onstar and @professor :+1:

Glad to have the Powercore Essential 20000 PD :blush:

1 Like

I edited the 2nd post with more details not shared previously.

It does confirm my overall general recommendations for portable chargers.

  1. carry the Powercore as small as possible to be just large enough to handle your worst case scenario. I often find that is more 10Ah than 20Ah.
  2. Use USB A to C port for maximum efficiency
  3. use the shortest USB cable for maximum efficiency
  4. plug your Powercore in early so it’s more being used to keep the device full than it is to recharge the device, then the current is less and cable losses less and the slower Wattage of A-C than C-C has no time loss as it’s low Wattage anyway at maintain-charge than recharge.

Carry a smaller Powercore, a short A-C cable and use it often.

Today I was out and about total of 8 hours, I went out on bike and walking and carried and connected my 3 year old Powercore II 6700, it has proved ample to get me through a long day. I finished with a fully charged phone and 1/3rd depleted 6700, I could have then gone on to survive overnight if required finishing next morning with both near depleted. I’d then need a higher Wattage wall charger to then recharge both quickly.

Respect to Anker for such a professional polite response. I count 1 error from Anker and 3 from the customer. Anyone count more? I think I’d be fired within a week in customer support.