I think this is the cheapest way to check your powerbank capacity and of course with lots of patience as well. In the video I am using the popular 2600mAh powerbank in eBay as an example.

Concept: Basically you charge the powerbank (full discharged first) and get the Amp reading from the start and again at the end when is fully charge. Then note the full charge duration of the powerbank. Once you got the duration and the two Amp readings you can calculate the mAh.

What you need?

1. Powerbank
2. USB current voltage meter, \$5 in eBay, also known as Charger doctor
3. USB power source such as USB AC adapter
4. Timer, clock or a stop watch
5. Continuous recording camera such as car dash camera. This is optional if you are lazy to keep checking full charge time

Here are the steps.

Step 1: Fully discharge your powerbank.

Step 2: Plug the USB voltage current meter to the USB power source.

Step 3: Begin charging the empty powerbank and start timer. Immediately take note of the Amp reading. You can use a camera to record.

Step 4: Note the last Amp reading just before it is fully charge because there will be no current when the powerbank is full. If you use a camera, you can check the last Amp reading.

Step 5: Once you get Amp reading and charge duration time. Here is you can calculate, I will show by example [as described in video]:

Start at 0s powerbank empty ------ 0.7A = 700mA
Last at 3hours 53min 5sec powerbank full ------ 0.34A = 340mA
So, average at 0.52A = 520mA Then you multiply 520mA with the duration in hours, which is 2,019mAh (520mA X 3.88h)

Here you go, my 2600mAh powerbank actually has 2,019mAh only.
This calculation is approximately 10% to 20% accurate, see additional note below. If you want to get more accurate measurement you have to record the amp at short intervals like (every 10 mins) or use device such Power Analyzer Pro.

Additional note: The average calculation is assumed on linear regression (to make it easier to explain and demonstrate), however the actual charging profile is a non-linear regression meaning the current decreases more over time. So if you plot an actual graph of current over time, you will get a non linear graph.

<p>For an awesome calculator that does all the work for you, check this: <a href="http://www.powerbankexpert.com/power-bank-phone-mah-calculator/" rel="nofollow">http://www.powerbankexpert.com/power-bank-phone-mah-calculator/</a></p><p>Just choose your device and power bank mAh and it will tell you how many charges you should get from your phone!</p><p>If you're not getting around the same amount of charges from your power bank, it might be an inferior product or faulty.</p>
<p>I bought a Samsung Power Bank EB-PN910BBE 9500 mAh capacity. I emptied the Power Bank and charge it with USB Charger Doctor attached between the charger and the Power Bank. The USB Charger Doctor only shows 9040 mAh when the Power Bank is fully charged. Is this normal? Maybe the KEWEISI USB Doctor is not very accurate? I wonder where the 460 mAh went to? </p>
<p>I heard that these powerbanks also have some effectivity only around 93-97% of their declared capacity. I think its ok.</p>
This is just for the charging of the power bank. Shouldn't you be measuring the output as you drain it to get a more accurate reading?
In my opinion, theoretically should be about the same. The powerbank was completely drain before measure charging.
<p>if I have a 20000 mah unit and charge a phone twice and an I pad once how can I find out what capacity is remaining ...can I use a multi meter or plug-in device that will tell me straight away??</p>
<p>?? </p><p>how is it SIMPLY possible to know how much juice is left in my powerbank unit. I cant go thru this process each time I pick it up to charge something with it.</p>
<p>Is posible to know how many charge is available on the power bank with any app?</p>
We used to use a battery powered clock and connect it to the battery while discharging at a measured rate. All you did was set the clock to 12 noon, use a voltage regulator and see where the clock stops.
<p>How do you discharge the battery? do you use a light bulb? </p>
<p>Nice, thanks for sharing this!</p>

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Bio: Tech nerd like web technologies and gadgets. Kitesurf on weekends and recently got involved in 3D printing technology.
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