USB Power banks are essential if you are traveling outdoors or just prefer the convenience of having your devices charging near you without having to hunt down a wall outlet. USB power banks are portable rechargeable batteries that can potentially recharge your phone or other devices dozens of times. I use a power brick at home religiously since there are no power outlets near my bed and I like to use my phone as an alarm clock.
Power bank capacity is determined by mAh (Milliamp Hours) but some power is lost due to efficiency (about 20%). The calculation to figure out how many times you can recharge your power bank is as follows:
(Power Bank Capacity) x 0.8 / mobile phone battery capacity = number of recharges
For instance the Anker Power Core has a 10,000 mAh battery. Below are the number of times you can theoretically charge each device:
| Phone | Capacity | Number of Recharges |
| iPhone 6 | 1810 mAh | 4.42 |
| iPhone 6s | 1715 mAh | 4.66 |
| iPhone 7 | 1960 mAh | 4.08 |
| iPhone 8 | 1821 mAh | 4.39 |
| iPhone X | 2716 mAh | 2.95 |
| iPhone XS | 2658 mAh | 3.01 |
| iPhone X Max | 3174 mAh | 2.52 |
| iPhone XR | 2942 mAh | 2.72 |
Power Bank 24000mAh Portable Charger HuaF is a larger battery pack that offers other nice features such as a flash light and 3 usb ports to charge up to 3 devices simultaneously.
| Phone | Capacity | Number of Recharges |
| iPhone 6 | 1810 mAh | 10.61 |
| iPhone 6s | 1715 mAh | 11.20 |
| iPhone 7 | 1960 mAh | 9.80 |
| iPhone 8 | 1821 mAh | 10.54 |
| iPhone X | 2716 mAh | 7.07 |
| iPhone XS | 2658 mAh | 7.22 |
| iPhone X Max | 3174 mAh | 6.05 |
| iPhone XR | 2942 mAh | 6.53 |
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