We are using Nuki on a frontdoor, with 4 people using Auto Unlock and Lock Operations frequently.
I would guess we have 10-20 operations per day, depends on weekday, school vacation etc.
I have a number of rechargeable NIMH batteries at home - from Ikea, Panasonic, Aldi… - I just use the one that is charged, never care about which one to use. The batteries usually last several weeks, I guess 6-8.
The warning is pretty reliable, we have never faced a situation where the Nuki didn’t operate anymore.
My personal take is: before starting to mount a cable on a moving door, with a power supply that has to be always connected, I stay with batteries.