What is my powerbank real capacity?

You have an original real capacity 10,000 mAh power bank, and that should charge your 2000mah phone about 5 times, right? Well, here is where the confusion begins.

This powerbank has 4 3.7V 2,500mAh batteries, together that equals 10,000mAh and this is correct. Modern slim power banks have thin lithium polymer batteries so are still based on 3.7V but can be built in smaller sizes.

But USB is 5 volts!

Inside powerbanks are 3.7V batteries, but the USB standard is 5V.  Between the battery and the USB socket is a conversion circuit and this changes the 3.7 V into USB friendly 5V. When converting to a higher voltage, you must also convert the mAh into the new voltage.

How to calculate theoretical USB output 

A simple equation can be used to convert the 3.7V into 5V.

ACTUAL 5V mAh = 3.7 X Advertised mAh / 5

For a 10,000mAh powerbank – 3.7 X 10,000 / 5 = 7,400 mAh

So a 3.7V 10,000 mAh powerbank really only supplies 7,400 mAh output at the 5V USB connection. So straight out of the box is a 23% reduction in the stated mAh.  This is not the actual level as there is also conversion loss.

What is conversion loss?

As you use your powerbank the circuit inside that converts 3.7V to 5V USB uses some energy and also creates heat. During this conversion, you lose some extra mAh.  There is a wide range in conversion efficiency and most brands don’t state the losses, Xiaomi has prized themselves on their conversion efficiency chips which are up to 98% efficient, meaning you only lose 2% off your battery power in the conversion. Some others can consume as much as 10% during conversion.

One thought on “What is my powerbank real capacity?

  1. Arup S says:

    I believe the information that you provide on this webpage is incorrect, since you are just considering the increase in voltage performed by the circuit inside the power banks. Even if the USB port functions at 5V, the battery inside the phone is rated the same (as with all Li-ion batteries) i.e., 3.7V and hence the capacity as stated by the phone manufacturer should be directly comparable to that of the battery. Hence the 23% reduction that you mention is not a reduction in the capacity but the current used for charging. Once inside the phone, the reconversion should make the capacities comparable. Unfortunately, for the few customers who are calling out the manufacturers, a lot of these manufacturers point them to this 23% reduction saying that you need to do your homework before purchasing. So, either the circuitry used by these manufacturers are horrible (which could lead to actual problems with the batteries, safety and what not), or else they are incorporating smaller (and cheaper) batteries in their power banks are false advertizing them.

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