I have been testing the Pi Zero with an ONN 6700mah battery. I’ve run it continuous for 19ish hours with sporadic use when the battery gets to 25% per the led indicator.
I have also used a Renogy 10w solar kit with an accessory adapter with a USB plug to charge the battery up. I don’t have a total time due to the rain and clouds I had here and my schedule. But it did charge up to 100% when I left it out for the morning I had full sun.