pianotuna wrote:
landyacht318 does your AGM behave in the same manner as BFl13's?
Yes and No.
When newer, below about ~750 deep cycles or so, amps would simply keep tapering to 0.0X if left at 14.7v indefinitely.
From 750 to ~1000 deep cycles it would not taper much if any below 0.3v at 14.4 to 14.7v, but remain steady(90Ah capacity). A high amp recharge from a well depleted state would return its ability to taper to 0.2 amps before rising, but many low and slow recharge cycles and it would stop tapering above 0.4 amps and plateau or slowly start rising.
Now in the 1200 deep cycle range, and approaching 6 years of age in November, the amps do not taper below 2.1 amps and once they bottom out they start rising, and so does battery temperature at that point.
High amp recharges at this point, from a well depleted state, do not change this minimum amperage at absorption voltage, but do affect voltage retention during subsequent overnight discharge cycles.
But what i find surprising is the voltage retention during overnight usage. For the Ah removed, the voltage retained under load has remained impressive. It is still better than any previous flooded group 27 or marine battery even when they were new, at least until ~55 to 60Ah from full. I can pull 55Ah from it at upto 2x the 20 hr rate load, and will still read 12.0+ volts under a 5 amp load and rebound to 12.15 range with most of the loads removed.
It can still accept 65 amps for more than 15 minutes before voltage rises to 14.7v when discharged below 50%.
if it were not for the voltage it falls to when engine starting, and the amps never being able to taper to 0.5% of capacity before beginning to rise again, I would proclaim the battery to be 'still going strong' but it has to be approaching the end, I assume.
I bought a UB12180 AGm battery Last December for when Mine can no longer start my engine on its own.
This Ub12180 battery was difficult to get to taper to 0.5% of capacity when new and rarely now either, though I do not cycle it often, mostly just hold it at 14.7v for a few hours each week on its own ammeter unless I use it to jumpstart someone else, then I recharge it immediately.
Once amperage at absorption voltage bottoms out, there, or above there, amperage instantly starts rising along with temperature and if I do not reduce voltage or remove charger, I assume both amperage and temperature would keep rising.
While I can't argue with plate thickness being an obvious attribute for a deep cycle battery, I also cant argue that this Thin Plate Pure Lead Northstar AGM battery has far exceeded my expectations as far as deep cycles accumulated and dual purpose ability. It is still able to easily meet my needs, as long as I ensure the regular true full recharge, and it can still easily start my engine 55Ah from full in mild/warm ambient temperatures.
When it does need replacement, I'll go well out of my way to acquire another, perhaps stepping up to a G31 instead of a 27, and pay top $ for it, even though I could have a lifeline g31-XT delivered to me fresh from West Covina, for similar price.