If the battery is only ever charged from solar and I uncharge it to the lowest safe level in the evenings, it lets me get the best possible return on my capital expense. How long it lasts doesn’t matter in this regard.

But in terms of using it for UPS purposes, it lasting longer would mean I won’t need to expend capital again as soon.

So I guess it depends on what you want out the battery.

I did some math when I bought the battery and it seemed it would probably pay itself back before needing to be replaced, but it was questionable at our energy prices.

I bought the system mostly for UPS reasons though, especially as I work from home and on a personal note, sitting in the dark several evenings a week or being unable to make coffee when you want, sucks.