Power bank Capacity vs Size and Weight
The capacity (mAh) is linked to the size and weight of the power Bank, so usually a bigger capacity also means bigger size and weight.
mAh means milliamp Hour and is a unit that measures (electric) power over time. It is usually used to measure the energy capacity of a battery. In general, the more mAh and the longer the battery capacity or battery life.
Li-Polymer battery cell based Power Banks are typically slimmer and lighter compared to Li-ion based Power banks, which usually can have a smaller total footprint then.
How much can the USB Power Bank charge?
How many times you can charge your devices depends partly of the PowerBank capacity (mAh), set against the battery capacity (mAh) of the devices you want to charge.
Smartphone batteries typically have between 1500-2500mAh capacity. More powerful devices such as iPad / Tablets are normally between 6000-12000mAh. You can usually find the battery capacity (mAh) ratings on your various devices, in the manual / manufacturer documentation.
For example the iPhone 8 has a 1821mAh battery, so divided up with a 10000mAh Power Bank, will theoretically give you 5.49 full recharges – but you cannot really calculate it that easy…
It also require energy to convert the power!
It also consumes energy to actually transfer / convert the power – both in the Power Bank and the recipient device. Secondly, there is also a natural loss in the cables and factors such as temperature, humidity, and not least wear on both ends come in to play.
In other words, you can not just divide the PowerBank capacity with the devices battery capacity. A rule of thumb says that about 15-25% goes to the above. In bad quality PowerBanks an efficiency loss of 25-50% is not uncommon.
You can roughly estimate the number of charges a given PowerBank can provide to your gadgets:
Real PowerBank capacity * conversion rate * phone battery health / phone battery capacity = total charge times
Example iPhone 8: 10000 x 0.8 x 0.9 / 1821 = 3.95 charge times (+/- 0.5-1 times)
Example Huawei P20: 10.000 x 0,8 x 0,9 / 3400 = 2.12 charge times (+/- 0.5-1 times)
Is your deviceon while being USB charged?
One should also remember that if the device is ON while beeing charged, it also means up to double power consumption. In this case the Power Bank both have to charge the battery and keep the device operated at the same time.
It may also give some varied results if you put different Power Bank up against each other, even though they may have the same specified capacity. The battery cells may well deliver 10000mAh (1A for 10 hours at the given voltage) – but in practice it constantly differ in both power bank and the receiving device. Some are more / less efficient or faster / slower at certain charging intervals, temperature and humidity is a factor, cables, wear and then there is the matter of ‘Overhead’: When the electronics (both in Power Bank and Receiver) report their battery as full and empty, there is actually still some available capacity at both ends, to protect the battery and ensure longer battery life.
USB PowerBanks with fake rated capacity!
A standard / inferior / cheap Power Bank will typically have a significantly poorer energy efficiency than a better PowerBank like the Chill Innovation. Basically this means that it waste more energy itself, and therefore less capacity will be available for the device you are charging.
Secondly, fake rated PowerBanks are very common in the market unfortunately. Since you cannot easily tell if you get the actual capacity (mAh) rating the maker is advertising – most minor or unknown brands choose to fake rate, in order to appear cheaper. For example it might be sold as a 10.000mAh PowerBank, but in fact only have poor cells with 5000-6000mAh inside.
To avoid being cheated like this, do not buy too cheap and go for the major reputable brands. they might cost a bit more, but you will get a much better performance vs price ratio in the end.