There are a few factors,
Temperature is one. Generally the cold contributes to a fast discharge for batteries.
Event Recording - Notifications
If you have your doorbell set to record and notify of all events it will use more battery processing those actions.
Cooldown period, if you have a lower cool down period the camera will capture more events, thus more actions and more battery discharge.
I have my doorbell set to only record and notify if the doorbell is pressed, with power save mode turned on and my battery has only dropped to 87% in about a month with temps being in the teens here.
I do have 2 other cameras that cover the area, so if you are wanting alerts for all activities, then you will see the battery drop faster.