Powerbank users often get mystified with the mismatch between the expected capacity of their purchased powerbanks and the actual number of charges that they get for their smartphones or tablets.
We expect to charge our 2000 mAH battery smartphone 5 times using a 10000 mAH powerbank as 2000 x 5 =10000. However, in reality, your phone battery will get charged about 3 times!!
A quick rule of thumb is to assume that the real world capacity of your powerbank is 2/3 of the theoretical capacity mentioned on the package. So for a quality 10000 mAH powerbank it will be about 6600 mAH and for a 26800 mah powerbank it will be about 18000 mAH.
Understanding Powerbank Capacity
The reason for this mismatch is that mAH is not a good unit to measure battery capacity when the voltages of the battery and charged devices are different. Li-ion batteries used in powerbanks output 3.7 volt but your phones’ batteries get charged at 5 volt.
mWH or watt-hours is the ideal way to measure a battery’s stored energy as it is voltage-indepanedent and takes into account the total energy of the battery.
So a powerbank with 10000 mAH capacity actually has 10000 mAH capacity at 3.7 volt. Total energy in such a battery in mWH will be 10000 mah x 3.7 volt = 37000 mWH.
When the output is at 5 volt, the Mah capacity of this battery will be lower. The capacity of the battery while charging at 5 volt output will be 37000 mWH divided by 5V or 7400 mAH.
In addition to this, energy is also lost during the conversion process from 3.7 to 5 volt, due to the resistance of the connecting cable, and during the charging process. You may have noticed that the phones often get warm and mildly hot during charging. This is simply electrical energy getting wasted as heat during the charging process and is unavoidable in any charging process.
Many other factors, such as ambient temperature and the exact chemistry of the powerbank and smartphone batteries also determine the real charging performance of the powerbank. Assuming a 10% loss (or 90% efficiency), this leads to an effective capacity of 7400 x .90 = 6660 mAH . This is approximately 2/3 of the on-paper 10000 mAH capacity of the powerbank.
As the actual charging performance may vary from device to device, you can roughly assume the 2/3 capacity number to calculate how many times your smartphone will get charged by your powerbank.
For example, a quality 26800 mAH powerbank like Anker PowerCore+ 26800 will have a real world capacity of 26800/.66 = About 18000 mAH. Hence, it will charge an Apple iPhone 6 a(1840 mAH battery) about 18000 / 1840 = about 9-10 times!
Similarly, a good 20000 mAH powerbank like RAVPower 20100 USB type C or Anker PowerCore 20100 will charge iPhone 6 about seven times and a quality 10000 mAH powerbank like Anker PowerCore+ 10050 will charge iPhone 6 about 3.5 times.
Maximising Powerbank Capacity
To extract maximum power from your powerbank follow the following tips –
Use Good Quality Powerbanks
Quality powerbanks have higher efficiency of up to 95% due to optimized circuits.
Use Quality Short Cables
Quality short cables have lower resistance and hence lead to less loss of power.
Use 1.A Regular USB ports if not in a hurry
Charging at 1.0 Amp regular ports will ensure greater efficiency than charging at fast-charging high current 2A or 2.4A USB ports.