I view manufacturer voltage recommendations as starting points, but rely on the hydrometer to tell me if my absorption voltage is high enough, and held long enough, in my particular usage/recharge regimen.
I had a petulant group31 USbattery whose sweet spot with a solar
only recharge was 14.9v absorption and then 15.3v float/Finish for the rest of the afternoon, when cycling 35 to 60AH nightly.
Even then it needed a 16v EQ for ~50 minutes every 14 to 20 cycles.
If it did not get these rather absurd voltages, but just 3 to 4 hours of 14.7v, its SG would quickly walk down each cycle, and be in the 1.220 range after 14 cycles. If I went longer between 16v EQ's then it took many hours at 16v before SG would rise to 1.275. 15.5v or 15.7v EQs would not raise the SG to the maximum. It needed 16v. I thought this was ridiculous, but witnessed it half a dozen times. 15.7 for 4 hours could not do what 16v could do in 1.
I wound up getting nearly 500 deep cycles from that battery
before taking it from service
. The cell closest to the (-) post was heating
up at the bottom.
is still being lightly cycled, as a 12v source in my workshop. No EQs in a year. Surprised really.