Pylontech batteries, utilizing a 3rd

I have 2 pylontech batteries, noticing on odd days in winter that house requires greater demand than 2 can provide.
Considering benefit of purchasing a 3rd but concerned about underusing that third battery which may ultimately shorten it’s lifespan.
I estimate 8 months of year a third battery is never needed, and then only periodically in the other 4 months.
Would this be detrimental to the third (or others for that matter) battery?
I believe using battery to DOD 80% each day is most efficient, am I right in that ?
A third would mean DOD for 8 months usage may only be 40 or 50% would this be detrimental ?

If you add a 3rd battery your will get longer lifespan. Lithiums are very good at keeping a charge and very good at working every day. But if you don’t work them they will not deteriorate.

You will see your Pylontech is rated for an amount of cycles it can do. Those cycles are measured in the full capacity of the battery. So if you have a 100Ah battery and use the full 100% SOC down to 20% SOC you have completed 0.8 cycles. If over a few days you use only 10% SOC, 20% SOC, 15% SOC, 35% SOC, 20% SOC, then you could use 1 cycle.
They do not have a memory effect.

So if you add more banks it will reduce the peak current draw (which can be bad for the battery) and your banks should last more cycles (thus many more days, years)


As Louis mentioned. Adding more batteries to a bank will only be better for the existing batteries.

Remember that batteries deteriorate faster the more you discharge them ( down to a lower SOC) and the faster you discharge them (more peak amps drawn). So if you add another battery, you reduce the load on the existing batteries, thereby extending the service life. You also don’t need to drain them as much… so also extending the service life.

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As said adding a third battery and taking your bank down to 40, 50% every day rather than the 80% you currently do with the 2 batteries, will actually be better for the health of your battery bank in the long run.

Thanks for the replies and explanations.
I have now ordered a third battery.
Thanks all.