The number of years your batteries will last will depend on how hard you use them.
With a lead acid battery, the deeper you cycle it, the shorter the life. A battery may have 2500 cycles if you take it to a 50% SOC. Where as the same battery could have 8000 cycles if you always keep the charge above 80%. If you were to cycle the battery once a day for 8000 cycles, based on keeping the battery above 80%, it should last for 22 years*.
Most lithium batteries boast that you can discharge them to a SOC of 20% without affecting the life of them. That means you just have to keep the batteries charged above 20%. This sounds good, but it is worth having a look at the number of cycles they have. Often it is 2500 cycles*. This will last the same amount of time as a lead acid battery that is cycled to 50% SOC (in the example above).
* Please note: different brands of batteries have different specifications. Please call our office for more information.