# how to test the capacity of power bank with RD USB tester

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RD tech
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how to test the capacity of power bank with RD USB tester

Hello, everyone, nice to see you:

Nowadays when we are traveling or on a business trip, we will take a power bank because we don’t have so many chances to charge our mobile phones on the outlet, and I know there are some people who will fall into panic when their phones are out of power, because that is who I am. A good power bank can charge a phone several times and that enough for a day.

However, not all of the power banks have good quality, do you notice that power banks with the same milliampere hour can vary quite a lot in terms of performance, for example: one power bank says its capacity is 30,000 mAh, and I have a iPhone with 2,900 mAh, so it can power up my phone 10 times theoretically, but actually, the power bank is out of power after 3 times. So that I can make sure the capacity does not match technical parameters.

Today I want to show you some methods to measure the capacity of a power bank.

1.Simplest way:

You can just use your power bank to charge your phone, because you know the capacity of your phone battery, so that the capacity of power bank=phone battery capacity*charge times.

The consequence is not so accurate but it is not far from the real capacity.

3.Scientific way:

Use a USB tester and a electric load to discharge the power bank from 100% to 0%, you can get the accurate consequence.

We use our USB tester(UM25/UM34/AT35) to test the capacity, HD25/HD35/LD25 are used to discharge,set the current 2A

and we can use this two way to caculate:

①capacity=measured mAh * output voltage/battery voltage/efficiency

②capacity=measured mWh/battery voltage/efficiency

note: mormally the output of the power bank is 5V, the battery voltage is 3.7V the efficiency is about 85%-90%

set the data group at group 1, so that the capacity measurement can continue work next time we power it up

here are the power banks:

balck power bank:16000mAh

yellow power bank:10000mAh

blue power bank(xiaomi):10000mAh

Here is the consequence:

Black power bank: 4223mAh/20441mWh

yellow power bank: 5076mAh/24691mWh

Blue power bank(xiaomi): 6202mAh/29910nwh

so the real capacity is (use  method 2)

Black power bank:20441mWh/3.7V/90%=6138mAh(16000mAh)

yellow power bank: 24691mWh/3.7V/90%=7415mAh(10000mAh)

Blue power bank(xiaomi):29910mWh/3.7V/90%=8982mAh(10000mAh)

of course you can use the first way if you like:

Black power bank:4223mAh*5V/3.7V/90%=6338mAh(16000mAh)

yellow power bank: 5076mAh*5V/3.7V/90%=7622mAh(10000mAh)

Blue power bank(xiaomi): 6202mAh*5V/3.7V/90%=9312mAh(10000mAh)

OK this is the way to caculate the capacity, and we use this to test, you can test it at home as well, go start,contact me if you meet any problem.

this is my shop on Aliexpress: https://rdtech.aliexpress.com/store/923042

Edited by: RD tech on 11/01/2019 - 23:25
RD tech
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this is my shop on Aliexpress: https://rdtech.aliexpress.com/store/923042

hank
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Location: Berkeley, California

I would really appreciate links to powerbanks that tested good.
I’m aware of the “quality creep” problem — that by the time you recommend something, the manufacturer will have cut corners to cheapen the product.
But any info would be welcome.

RD tech
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Last seen: 28 min 33 sec ago
Joined: 08/27/2016 - 04:34
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hank wrote:
I would really appreciate links to powerbanks that tested good.
I’m aware of the “quality creep” problem — that by the time you recommend something, the manufacturer will have cut corners to cheapen the product.
But any info would be welcome.

thank you for message
I just provide a way to avoid bad power bank

this is my shop on Aliexpress: https://rdtech.aliexpress.com/store/923042

RD tech
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Last seen: 28 min 33 sec ago
Joined: 08/27/2016 - 04:34
Posts: 580

hank wrote:
I would really appreciate links to powerbanks that tested good.

we bought it from XiaoMi official store on Taobao