The lifespan varies depending on the quality and how well you take care of them. For example, when you store the units in high temperatures, they will get damaged fast than when you place them in a cool environment.
Dispose the batteries correctly: When the units die, dispose them properly to avoid problems. They contain heavy metals that can be explosive or flammable. To protect your property avoid burning, puncturing, or dismantling them. The best way of disposing them is taking them to a company dedicated to recycling them.