I spoke with Bruce Essig at Odyssey years ago, and he was rather adamant that if one could not Float their battery at the recommended temp compensated voltage, to not float it at all.
When I fully charge my Northstar, holding absorption voltage until amps taper to really low levels, or start rising again, then float my Northstar too low, it discharges slightly.
I know this as when I bump pressure back upto 14.7v, it takes a period of time before amps again taper to the low level that caused me to declare fully charge previously, then turning voltage down to the too low of float voltage. This indicates the battery was discharging slightly, when floating too low
for those insisting on exact float voltage and with a tinkerer mindset:
hook this Buck converter to the output of an old 19.5vDC Laptop power supply:
Say the supply is rated for 6.5 amps output. This device will step down the 19.5v to whatever one chooses, via one potentiometer, and the other potentiometer allows one to limit the maximum amperage
put this on the output of the buck converter so you can see voltage and amperage and amphours/ watthours.
They get a little inaccurate under 0.4 amps, reading low, but is 'good enough' depending on where one sets that line.
it should be noted that on each and every AGM i have cycled to death, at near end of life, amps will not taper to the low levels they once did.
At too high a float voltage in this end of life stage, the battery will warm up, and the amperage required to maintain that voltage, will keep rising, even with the warming battery, and then that same float voltage would be too high even if the battery was still healthy.
Too high a floast voltsage on an end of life AGM battery, can lead to thermal runaway, which can be dangerous.
think of all the AGM in the Uninterruptible power supplies that are melted and stinky.
Too low a float voltage is safer, on an end of life battery.
Makes charger manufacturer retained lawyers happy, but makes newer healthy batteries age faster.