In fact the internal battery is 3.7V, and a booster circuit enables delivering 5v, but suddenly the power is only 1000mAh 5v on ...
There is therefore in my misrepresentation of the product, but it is nevertheless indicated on the box as you can see here:
[...]
My smartphone has a battery 3.7V / 2500mAh, and this external battery only allows to load the tier.
