My previous AGM, in its final 6 months of deep cycling life would never approach 0.5% of capacity@ 14.7v, but stall above that and then amps would start rising.
Its replacement just keeps tapering to 0.0x amps at any voltage if left at absorption. when i lower it to 13.6v at 0.5%, and leave it overnight, when I crank it to 14.7v the next day it tapers to 0.0x, the X being as i can't accurately measure amperage less than that.
I've two smaller chinese AGMS, 18 and 22Ah, The Ub12180 and UB12220. Both when newer refused to actually taper to 0.5%, but after a few deep cycles would. One of them will not go below 0.5%, but the newer one will. Both find bottom amps and bounce. amps start rising at some point. I try to not let this happen and at 0.5% call it macaroni and remove them or lower voltage to 13.6v.
The screwy 31, a flooded marine battery, at the end of its life exhibited similar behavior, amps would taper to a certain point at absorption voltage, then start rising.
My charging sources are constant voltage, not constant current, other than when the the charger's output terminals are still below the absorption voltage I have chosen.
If I try to achieve constant current I fiddle my voltage potentiometers, keep raising them from a low point to keep the amps in the 5 per 100Ah of capacity range, but very rarely bother. The times I do this are on the smaller agms when I dont want them feasting on 25+ amps. the 18AH AGM says 5.4 amps max, the 22Ah AGM says 6.6 amps max. I double this rate almost each recharge but tripling/quadrupling that amount is not something i do other than to see what the quench amperage would be, as a data point, for future reference as they age.
Neither small Chinese AGM warms significantly when doubling the maximum recommended rate. I'd not double the recommended rate in 90f+ ambient temps and I might not choose to do so once they have aged and accumulated more cycles.
I don't have any more flooded batteries to cycle, but adjustable voltage charging sources and the hydrometer removed all the mystery and guesswork with the screwy 31.
