The battery life of an electric toothbrush will vary depending on factors such as brand, model, frequency of use and number of charges. Generally speaking, the battery life of an electric toothbrush is usually between 1 and 3 years, but the specific replacement time depends on the following factors:
1. Frequency of use: If you use an electric toothbrush multiple times a day, the battery may run out faster. Conversely, battery life may be extended if used infrequently.

2. Charging method: Some electric toothbrushes use rechargeable batteries, while others use replaceable batteries. Toothbrushes with replaceable batteries may need to replace the batteries more frequently.

3. Battery type: Different types of batteries (such as lithium-ion batteries, nickel-metal hydride batteries, etc.) have different lifespans and charging cycles, so the replacement time will also be different.
4. Usage environment: Harsh usage environments such as high temperature and humidity may affect the life of the battery.
5. Charging habits: If you frequently overcharge or undercharge, it may affect battery life.
When you find that the battery life of your electric toothbrush is significantly shortened and cannot meet normal use time, or the battery cannot be charged properly, it may be time to consider replacing the battery. It is recommended that when the battery has problems or its life is gradually reduced, contact the customer service of the electric toothbrush brand for advice on battery replacement or repair. When replacing batteries, be sure to choose the original battery for your toothbrush model or a certified replacement battery to ensure safety and performance.