Well, it is quite difficult to predict accurately how long will the battery last in welding helmets. This also depends on the factors like how often you use it and what features it supports. We also have helmets that have solar cells in addition to the batteries, these facilitate the darkening of the filter when working under the sun. When you notice that your lens is not working as required, it is Time to replace the batteries. Considering the availability of the cells, they are available online and also in the stores, but it is essential to ensure that you get the right battery for your model. Generally, a good battery lasts for about three years on being used continuously for welding purposes.