That's the problem with tenders, though, the constant float sulfates the battery. Too low of a voltage and you get negative plate, hard sulfation, which is one of the main aging affects for lead acid batteries. Everyone worries about being too high, which can be an issue but mainly because of overheating the battery and causing the electrolyte to boil, so they use dumb chargers with too low of a float voltage. If you have access to an engineering school library find the Journal of Power Sources has had some good submissions over the years about aging of cells and benefits of active equalization for float and recovery.
A couple of years ago worked on a project that included a charging circuit to de-sulfate flooded batteries. This was for power monitors in cell towers but the theory holds generally. You'd be surprised at how long a cell site could be offline before someone notices, particularly remote ones. So this company sells monitors that sense a few critical things, power in, power out, transmit level to judge site status and notify someone. This already exists, most all commercial transmitters have remote monitoring, but what these guys were doing was a lot cheaper and simple.
Anyway, even without remote sensing cell site UPSes go through tremendous numbers of batteries (they claimed there are 500,000 UPS batteries in use at cell sites across the U.S.) and increasing life even marginally makes a difference in bottom line. The algorithm they wanted implemented ran an equalization every 2 weeks, but I couldn't tell you what the real world results have been. I know they still build plenty of them, so I presume they are selling quite a few. I'll see if I can find something out. The essential circuit we came up with was a current interrupting equalizer running with 2.4V/cell doing 15 second overcharges with a 20 second rest. IIRC the overcharge was 1.1C, so it depended on the battery they used in the bank, but we'd be at 5 to 10 amps per battery. The charger itself was 4 stages, bulk, absorption and float which followed the standard curves, the special stage was the conditioning one.
