Portable Battery charger case has two regular standard of capacity , one is the battery capacity, one is the rated capacity. 

Why exist this difference?

The most important reason is the conversion rate. Because most of power bank's battery voltage is 3.7V, and power bank needs to increase the voltage to 5V when charging the mobile phone, which making the power bank's conversion efficiency only 3.75/5=74%, Also include generated heat when battery voltage boosting, and various of wire consumption, Electricity and self-consumption. these points add up to account for 30%-40% of the power of the mobile power source.
So the 5,000mAh power bank can really be used by us only about 3000-4000mAh.

Also, The conversion rate of the entire mobile power industry is basically in the range of 60%-70%. Please kindly noted.

20000mAh Portable Solar Power Bank Charging Poverbank Three defenses External Battery Charger Strong LED Light Double USB 

usage method:

Stand alone switch, start charging

How to use LED :

1. Double click twice quickly the switch quickly to turn on the LED light

2. Click Fast Close again to change the brightness frequency

3. Double click twice quickly the switch quickly to turn off the LED light

Product name: Power Bank 

battery capacity:20000mAh
Usable capacity: 4000-6000mAh
Material: plastic ABS +TPU

Specification:

Product Features
1, super waterproof grade (IP68) the highest level of waterproof
2, waterproof, dustproof, anti-drop, shockproof, anti-bracket function (five anti-upgrade version)
3, built-in lithium-ion polymer A batteries (explosion-proof)
4, Solar energy charging power is very low .
The charging power is about 0.8W-1.3W
5, composite materials, PC flame retardant materials, safe and worry-free
6, using super bright military LED double light design and SOS emergency signal light (super light)
7, dual USB interface, over-current and over-discharge short-circuit protection (device safety)
8, imported digital chip, high conversion rate, energy storage superhero first class
9, the back shell compass design; configuration mountaineering buckle, can be hung on the backpack

Package Included:

1x Power Bank

1x Charger Cable

1x User Manual