60 hours, approx. 3.57 hours per 1000mA (57.14 hours total) 16000mah capacity.
I am very happy with the power bank but it charges slowly, this is more a limitation of solar cells and the size.
Once charged it has a fast and a slow USB port, I am very happy with the fast port for charging my iPhone 7 in around 2 hours.

Good day
Can the powerbank also be charged from the mains when the sun is not shining for a long time?

Grüezi Frau Witzig, with optimal sun conditions and optimal setting angle to the sun approx. 92 hours at our latitude. Personally, I am very satisfied with this power bank. If the charging time with the sun is too long for you, there is still the possibility to charge it with an external solar panel 21 or 24 Watt 5 Volt.

I estimate at least 2 days for a full charge, but expect 4 days....

I have never had it completely empty and therefore cannot give an exact figure. However, it charges with 280mA in the sun, which is not fast if you extrapolate. Absolutely ideal for my purpose.