A quick question about battery lifespan

Re: A quick question about battery lifespan

In general, Telecom batteries were designed to "float" for 40 years with the (few times a year) of fairly shallow discharge (some batteries, if I recall correctly, some long life telecom were designed for to discharge to only 85% or 80% for frequent cycling).

Telecom battery banks were not usually defined/installed in system for daily cycling (emergency use + genset).

From what I have seen and looking at the typical deep cycle battery specification... If you design one system to deep cycle 50% every day vs 25% every day--Yes, the 2x larger bank will last ~2.2x longer. So--in pure dollars out of pocket, a larger bank will cost about the same amount of money when spread out over the years. What you gain is the hassles of changing 2x your bank (maybe) every ~10 years vs your 1x bank every ~5 years (assuming deep cycle batteries designed for load and are properly recharged, etc.).

You can also go with Fork Lift type deep cycle batteries which may last 20 years of deep cycling--But you will probably need more solar panels (bank has higher self discharge, less efficient charging) and more water than a Tojan RE battery bank.

At this point--Darned if you do, and darned if you don't.

If this is a new installation--I tend towards recommending buy less expensive batteries and keep the battery bank a bit on the smaller side (i.e., 2 days of backup power to 50% discharge vs 3 days of backup/no sun to 50% discharge) and see how things work.

If the bank gets killed (something left on, kids really like playing XBox, etc.) you don't feel as bad replacing after 3 years. And, by that time, you will have a better idea of your load requirements--so you can adjust bank capacity/solar array/backup genset to match for the next 10+ year bank.

-Bill