I recently crafted 25 sensor boxes that I then put out onto the yard to get an initial GNSS fix with a full battery (5000mAh). I seriously had a couple of boxes run out of battery (2.5 days) before getting their initial GNSS fix. I am not sure whether the proximity of lots of electronics messed up their reception, but it was the worst TTF I’ve had so far. Usually it takes <4 hours, but yes, it can take very very long!
When I charged them a few days later and put the remaining two in the window sill, they got a fix in a few hours.