FAQs Power Bank Charging

Here we explain the relationship between the stated capacity of a Power Bank in mAh and the number of times a user can charge their mobile or tablet device before a Power Bank recharge is required.

Power Bank Capacity

Power Banks have a capacity rated in mAh (milliampere hours). This is a measure of the charge stored within the Power Bank. The industry standard is that the total cumulative charge stored within the Power Bank cell(s) is stated as its capacity.

It is sometimes incorrectly assumed that all of the charge within a Power Bank can be transferred to the battery of the device it is charging, with no loses.

The physical reality is that energy is lost at different stages as charge is transferred from the Power Bank cells to the recipient's device.

This is the same with all Power Banks, regardless of the brand. Below is a graph outlining how many times each capacity can charge popular devices before you need to recharge the Power Bank.

Charge Times *
4
3
2
1
7%
iPhone 13
7%
iPhone 14
7%
iPhone 15
6%
Samsung S22
6%
Samsung S23
6%
Samsung S24
16%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
20%
iPhone 13
19%
iPhone 14
19%
iPhone 15
17%
Samsung S22
16%
Samsung S23
16%
Samsung S24
44%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
43%
iPhone 13
42%
iPhone 14
41%
iPhone 15
37%
Samsung S22
36%
Samsung S23
35%
Samsung S24
98%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
51%
iPhone 13
50%
iPhone 14
49%
iPhone 15
44%
Samsung S22
42%
Samsung S23
41%
Samsung S24
15%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
59%
iPhone 13
58%
iPhone 14
56%
iPhone 15
51%
Samsung S22
48%
Samsung S23
47%
Samsung S24
33%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
65%
iPhone 13
64%
iPhone 14
63%
iPhone 15
57%
Samsung S22
54%
Samsung S23
53%
Samsung S24
49%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
86%
iPhone 13
85%
iPhone 14
83%
iPhone 15
75%
Samsung S22
71%
Samsung S23
69%
Samsung S24
95%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
98%
iPhone 13
96%
iPhone 14
94%
iPhone 15
85%
Samsung S22
81%
Samsung S23
79%
Samsung S24
22%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
5%
100%
iPhone 13
100%
iPhone 14
98%
iPhone 15
89%
Samsung S22
84%
Samsung S23
82%
Samsung S24
31%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
17%
100%
iPhone 13
15%
100%
iPhone 14
13%
100%
iPhone 15
5%
100%
Samsung S22
97%
Samsung S23
95%
Samsung S24
66%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
29%
100%
iPhone 13
27%
100%
iPhone 14
24%
100%
iPhone 15
12%
100%
Samsung S22
7%
100%
Samsung S23
5%
100%
Samsung S24
93%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
31%
100%
iPhone 13
29%
100%
iPhone 14
26%
100%
iPhone 15
14%
100%
Samsung S22
8%
100%
Samsung S23
6%
100%
Samsung S24
97%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
4
3
2
1
52%
100%
iPhone 13
50%
100%
iPhone 14
47%
100%
iPhone 15
33%
100%
Samsung S22
26%
100%
Samsung S23
23%
100%
Samsung S24
46%
100%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
5
4
3
2
1
96%
100%
iPhone 13
93%
100%
iPhone 14
89%
100%
iPhone 15
71%
100%
Samsung S22
62%
100%
Samsung S23
58%
100%
Samsung S24
46%
100%
100%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
7
6
5
4
3
2
1
5%
100%
100%
100%
iPhone 13
100%
100%
100%
iPhone 14
93%
100%
100%
iPhone 15
66%
100%
100%
Samsung S22
52%
100%
100%
Samsung S23
46%
100%
100%
Samsung S24
92%
100%
100%
100%
100%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.
Charge Times *
9
8
7
6
5
4
3
2
1
92%
100%
100%
100%
iPhone 13
86%
100%
100%
100%
iPhone 14
78%
100%
100%
100%
iPhone 15
42%
100%
100%
100%
Samsung S22
25%
100%
100%
100%
Samsung S23
17%
100%
100%
100%
Samsung S24
92%
100%
100%
100%
100%
100%
100%
100%
100%
Kindle
* These charge times assume no degradation of the battery in the smartphone, tablet or eBook and should be considered a guide. Actual performance can vary.

Where is the energy lost?

As charge moves from the Power Bank to the device (the connected phone for example) energy is lost at various stages on its journey:

1) The industry standard cell(s) used within the Power Bank commonly output 3.7 Volts. This voltage has to be boosted up to 5 Volts via the Power Bank's internal circuitry as this is the standard voltage of a USB interface. Energy losses during this boosting phase are around 10-15%.

2) As the energy leaves the Power Bank, it will encounter some electrical resistance within the cable. Cable quality and cable length are important factors. For example a cable of 1 meter in length made from low quality wire, can result in significant energy loss due to its high resistance value.

3) As the charge arrives at your device the voltage will again be changed, this time stepping down from 5V to around 4V to match the requirement of the device’s internal battery. This conversion leads to further energy losses.

4) The characteristics and behaviour of the circuitry in your connected device influence the amount of energy lost at this stage. If your device has a fast charge function, its likely energy transfer will be less efficient than a standard rate of charge as efficiency has been traded off for speed. Lower quality (often cheaper) devices tend to be less efficient overall at energy conversion, even at normal charging speeds.

5) Finally the quality and longevity of the battery within your device plays an important role in the amount of charge it can successfully capture. If for example your phone is 1-2 years old, it likely charges much less efficiently than a new phone whose battery has not endured as many charge cycles. Effectively, each charge cycle makes the process of charging on the next cycle fractionally less efficient and over time these inefficiencies add up.

What happens to the lost energy?

Energy is typically lost in the form of heat, and this is why devices being charged typically become warm. All our Power Banks contain multiple levels of protection, one of which shuts down the Power Bank should the temperature move outside expected operational levels.

Still have some questions?

We’re here to help. Simply call (650) 938-3500 (US) or contact us via this page