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FAQsPower 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. 

The graph below shows you how many times each capacity can charge popular devices before you need to recharge the Power Bank. You can select different capacity options from the dropdown menu.

Charge Times *
4
3
2
1
13%
iPhone 8
9%
iPhone X
8%
iPhone 11
8%
Samsung S8
8%
Samsung S9
7%
Samsung S10
17%
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
38%
iPhone 8
25%
iPhone X
22%
iPhone 11
23%
Samsung S8
23%
Samsung S9
20%
Samsung S10
49%
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
83%
iPhone 8
56%
iPhone X
49%
iPhone 11
51%
Samsung S8
51%
Samsung S9
45%
Samsung S10
7%
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 8
66%
iPhone X
58%
iPhone 11
60%
Samsung S8
60%
Samsung S9
53%
Samsung S10
26%
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
14%
100%
iPhone 8
76%
iPhone X
67%
iPhone 11
69%
Samsung S8
69%
Samsung S9
61%
Samsung S10
46%
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
27%
100%
iPhone 8
85%
iPhone X
74%
iPhone 11
77%
Samsung S8
77%
Samsung S9
68%
Samsung S10
63%
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
67%
100%
iPhone 8
12%
100%
iPhone X
98%
iPhone 11
5%
100%
Samsung S8
5%
100%
Samsung S9
89%
Samsung S10
14%
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
89%
100%
iPhone 8
27%
100%
iPhone X
11%
100%
iPhone 11
15%
100%
Samsung S8
15%
100%
Samsung S9
5%
100%
Samsung S10
43%
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
97%
100%
iPhone 8
32%
100%
iPhone X
15%
100%
iPhone 11
20%
100%
Samsung S8
20%
100%
Samsung S9
5%
100%
Samsung S10
53%
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
27%
100%
100%
iPhone 8
52%
100%
iPhone X
33%
100%
iPhone 11
38%
100%
Samsung S8
38%
100%
Samsung S9
22%
100%
Samsung S10
91%
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
50%
100%
100%
iPhone 8
68%
100%
iPhone X
46%
100%
iPhone 11
52%
100%
Samsung S8
52%
100%
Samsung S9
34%
100%
Samsung S10
21%
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 *
4
3
2
1
54%
100%
100%
iPhone 8
70%
100%
iPhone X
49%
100%
iPhone 11
54%
100%
Samsung S8
54%
100%
Samsung S9
36%
100%
Samsung S10
25%
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 *
4
3
2
1
95%
100%
100%
iPhone 8
98%
100%
iPhone X
73%
100%
iPhone 11
79%
100%
Samsung S8
79%
100%
Samsung S9
58%
100%
Samsung S10
79%
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
81%
100%
100%
100%
iPhone 8
55%
100%
100%
iPhone X
23%
100%
100%
iPhone 11
31%
100%
100%
Samsung S8
31%
100%
100%
Samsung S9
5%
100%
100%
Samsung S10
88%
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 *
8
7
6
5
4
3
2
1
91%
100%
100%
100%
100%
100%
iPhone 8
96%
100%
100%
100%
iPhone X
46%
100%
100%
100%
iPhone 11
59%
100%
100%
100%
Samsung S8
59%
100%
100%
100%
Samsung S9
16%
100%
100%
100%
Samsung S10
58%
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.
Charge Times *
10
9
8
7
6
5
4
3
2
1
61%
100%
100%
100%
100%
100%
100%
100%
iPhone 8
10%
100%
100%
100%
100%
100%
iPhone X
46%
100%
100%
100%
100%
iPhone 11
62%
100%
100%
100%
100%
Samsung S8
62%
100%
100%
100%
100%
Samsung S9
8%
100%
100%
100%
100%
Samsung S10
76%
100%
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.

Custom Portable Charger

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