What Does Battery 'Design Life' Mean?
All batteries have a design life that can be used as an indicator as to their functional service life.
The standard design life is 5 years, although 10, 15 and even 20 year design life batteries are available.
Whether or not a design life is met or not will depend on a number of factors including the number of charge/discharge cycles, ambient temperature, maintenance and overall quality of the battery itself.
For a 5 year design life battery, replacement should be considered around year 4, and for a 10 year design life battery replacement should be within year 8.