Your Ring battery should last between 6 to 12 months on a single charge. Whether you fall on the high or low end of this spectrum will depend on how much activity your doorbell is recording (you can set the motion sensitivity lower, for example, to reduce the amount of footage that is captured). In our personal experience we had to change the battery around the 8-9 month mark on our Ring Doorbell Pro 2. Other factors that could affect your battery life include cold temperatures, particularly in winter if the temperate falls to 40°F or lower.