A Power bank is also known as battery charger. It is used by peopel when they are going out without a Travel charger or Car charger for emergency use. Initially it was powered by dry cell batteries for old Nokia phones without a touch screen. As li-ion battery cell technology developed, it was made up of li-ion battery and Li-polymer battery cells. During this time, the power bank capacity was high and could be used for touch screen smart phones or tablets.

You can find 1800mah, 2500mah, 4000mah, 8000mah , 12000mah Power Bank in retails. So, there goes the question, how can I know the capacity of power bank I am going to purchase? How can I know it will meet my requirement or not? Here we go some useful tips from us:

We buy a power bank with capacity of 4000mah. Normally it would be about 15-20% less for the output capacity, some even good ones only 10% or less loss. Why this happen? The capacity of the power bank is counted only by the battery cell, 4000mah. But the output should go from battery cell to PCB board with circuits and ICs, then to charging cables, then to your phones. During this process, there will be about 20% loss. You are right, it is crazy to know this. So, the real capacity is about 4000mah * (100% – 20%) = 3200mah.

Let’s continue to charge your phone now. If your iphone is 1850mah battery, there should be 3200mah / 1850mah = 1.73 times. We say, 1 time full and 70% the 2^nd time.

But, I want to let you know, this is just in theory. Why? Actually in our charging process, the phone is still on. It needs power to support the phone working. Under normal condition, it can only charge this phone 1.4 ~ 1.5 times.

Question: I bought a 4000mah power bank, I can charge my phone with 1800mah battery 2 time FULLY.I am not joking. Why?

Answer: this may caused by the following: 1) the power bank capacity is 4000mah or more, and the loss is less than 20%. It will charge your phone 2 times full. But Lider Industrial Ltd will let you know that, things like you described are very slim. 2) Your phone is 1800mah, but after a year of usage, the real phone battery capacity dropped to 1600mah or even lower, 1400mah. So, 4000mah*80%/1600mah (phone label may say 1800mah) = 2 times full. The 2^nd one is the regular rule.