I buy them for all my customers with on premises servers and the bill for replacing them in mine kind of gets split up in the labor cost of swapping everyone else. I do them every couple years after finding that there's a pretty steep decline in capacity in the third year pretty much across the board. I usually keep the old set on hand for a replacement cycle just in case one dies, but that's only happen to me one time. It's easy to be proactive about it and it gives me an incentive to at least do a bunch of billing in October.
I did not know that batteries declined so much. Would you would replace personal UPS batteries every two years if they were at your residence?