# How To Calculate Actual mAH of Your Powerbank, Methods.

What is powerbank charging efficiency?

Ever wonder why charging cycle of your powerbank does not match the actual battery capacity on your mobile phone? We're you sceptical about the integrity of powerbank capacity? Worry not! We are here to explain to you the right way of calculating a powerbank's capacity.

A common misconception:

The unit milli ampere-hour (mAh) is generally used to describe the capacity of a battery. One common misconception is that we can simply divide the capacity of a battery by the capacity of a smartphone/tablet to figure out how many cycles we can use this power bank to charge the smartphone/tablet. However, that is not the correct algorithm.

Converting into Watt/hour:

Simply put, Ampere-Hour (mAh) is a measure of electric charge, which represents the capacity of a battery, while Watt Hour (Wh) is a measure of electric energy.

Watt-Hour = Ampere-Hour x Voltage

A battery of 10400mAh means this battery can provide a total charge of 10400mAh at a specific voltage. As to a Lithium-ion battery most of its charge is exchanged at around 3.7V. Thus the total energy of a 10400mAh battery is theoretically 10400mAh x 3.7V = 38480mWh, which is approximately 38Wh.

Calculating the charging cycle of a powerbank:

A simple calculation formula would be as following:

Powerbank mAH x 3.7v (Output) / 5V (Mobile Voltage) - 10% Circuit Consumption

Here's an example:

Take power bank Nexus as an example.

Nexus consists of a 10400mAh Lithium-ion battery. When we use a Nexus to charge other devices, like using many other power bank products, the output charge voltage is converted to 5V.

Thus the total available output electric charge is 38480mWh / 5V = 7696mAh in theory. The internal circuit must consume some power so the efficiency cannot be 100%. Given that the actual discharge efficiency of TL-PB10400 is about 90% under 1A current, TL-PB10400 can actually "push out" a total electric charge of 7696mAh *0.9 = 6926mAh.

Note: The discharge efficiency is less than 90% under 2A current.

Now you might divide 6926mAh by your smartphone's capacity to figure out the possible charge cycles. For example, 6926mAh should be able to fully charge a 2600mAh device for 6926mAh / 2600mAh = 2.66 times. But that's still under the ideal conditions.

*Now, all the charging cycle indicators you saw on our website are based on this calculation, based on optimum usage at ideal conditions. They may vary from device to device over the lifespan of a battery.