It's incorrect to test the capacity with USB tester, the power bank is 3.7V, while the USB tester is 5V.
The normal energy of 30000mAh battery capacity power bank is 30000mAh*3.7V=111000mWh, when it charges phones, the output will be 3.7V/5V*30000mAh=22200mAh.
ASOMETECH 30X Power Bank
Product Cell: Polymer Cell
Power display: LED Display
Powerbank Weight: about 544g
Product Size: 155*73*32MM
Battery Capacity: 30000mAh
Micro/Type-C/Lightning Input: 5V1A-5V2.1A
2xUSB-A Output: 5V1A-5V2.1A
Product features: Three inputs, Two outputs
Product Color: Black/Red/White
Compatibility: For 99% of electronic devices
Note:
It's not correct that some buyers test the capacity of our power bank with USB tester and thought the capacity is less than we marked.
Why the battery capacity is 30000mAh and the rated capacity is only 22000mAh?
There are two reasons:
1. Law of conservation of energy
The unit to measure the power bank is not only the mAh, but also the mWh (mAh*V=mWh).
The voltage of power bank is 3.7V according to lithium battery standard, while most mobile phones, computers and other mobile devices are the standard 5V voltage for USB interface. Therefore, the power bank needs to boost the voltage to 5V before charging the phones.
The normal energy of 10000mAh battery capacity power bank is 10000mAh*3.7V=37000mWh, when it charges phones, the output will be 3.7V/5V*10000mAh=7400mAh.
The normal energy of 20000mAh battery capacity power bank is 20000mAh*3.7V=74000mWh, when it charges phones, the output will be 3.7V/5V*30000mAh=14800mAh.
The normal energy of 30000mAh battery capacity power bank is 30000mAh*3.7V=111000mWh, when it charges phones, the output will be 3.7V/5V*30000mAh=22200mAh.
2. Energy loss during charging
The power bank cannot output the 100% energy during the process of charging due to the energy loss of boosting voltage. And the conversion rate will be influenced by the output current. Generally, when the output current is 1A, the conversion rate is higher than when the current is 2A.
Please note that the conversion rate is basically in the range of 60% -70% in the entire power bank industry.
There are two capacity standards for power bank, one is the lithium battery capacity (the capacity we write in our product title), and the other is the rated capacity (the capacity measured by buyers with USB tester).
For example, the power bank of some famous brands have a rated capacity of 18,000-19500mAh for their 30,000mAh battery capacity.
Google it for more detailed information about battery capacity and rated capacity.
