I have experience with an 18Ah AGM that weighs the same as the UPG UB12180, 11.4 lbs.
It, by itself, when I first got it ( 5 months old at that point and 12.82v) and cycled deep once and charging it until amps stopped tapering at 14.7v, was able to start my cold 5.2 liter gas engine, by itself, just barely, in warm ambient temperatures. My meters registered a nearly an 1800 watt surge and voltage dropped as low as 7.9v
I have not repeated this experiment, yet, 15 months later. The battery full charge resting voltage is 13.16 after 24 hours, 13.13 48 hours later and seems to lose about 0.01v each day there after
I wanted 24v of portable battery, and recently got a UPG UB12220, a 22 amp hour AGM battery of the same exact dimensions as the 18AH battery, but weighs 14.1Lbs, 2.6lbs more.
I've only got a few shallow cycles on it so far, but these two AGMs of dissimilar age, and weight, and capacity, did not discharge evenly in series, nor do they charge properly in series @29v, I stopped that quickly, and now charge them separately. But uncycled batteries always behave weirdly that initial charge discharge cycle and less so each additional one.
The 22Ah agm loses surface charge voltage much faster but both settle to within 0.02v of each other a day later.
Are these Asian UPS sized AGMs worth it, even in the larger common sizes, 35, 55 75 100AH? Impossible for me to say, I only have experience with an older 12Ah one, an 18AH(Ub12180) and now a 22Ah(Ub121220). The 12 is the only one that failed, many many years ago after many years of use, and highly suspicious initial recharging regimens.
They meet my needs and expectations, and I Will recharge them at more than 2x the recommended maximum rate without fear, in mild ambient temperatures, but not leave them unattended with a high absorption voltage for hours on end either.
The well depleted 18Ah battery accepts 38 amps peak from a 40 amp adjustable voltage charging source set at 14.7v and then levelled off at 32 amps, dropping to 25 amps some 5 minutes later. I didn't notice any case surface heating in that time, but lowered voltage/pressure/amperage to 10 amps and walked away. (5.4 amps maximum recommended)
It is not hard to pry off the lid of These. When one does they see 6 rubber caps, kept in place by the lid and the glue lines are designed to obviously keep the same general pressure across all 6 cell tops.
Remove a rubber cap under this lid, and one can try to see into the cell via a 5 to 7mm aperture.
The venting pressure is therefore Imprecise at best, and could be changed with the pressure on the top of the battery, holding the lid over the cell tops tightly. I had a few rubber caps pop off and go a fair distance when I pried on the lid.
I might add drops of distilled to each cell on the older one, its voltage retention after charging and surface charge retention 2 to 6 hours off the charger seem abnormally high, just like a flooded marine battery low on water.
The 'new' 22 Ah AGM was made the 19th week of 2019, when I got it, two weeks ago, arrived @ 12.81v@67f. I think that is a huge issue with these Asian UPG/UB batteries and their clones and relabels, they sit on a shelf for who knows how long before placing 'click order' and they certainly came over on the slow boat, and were they fully charged when they left?.
They do not have the great low self discharge of high$$ AGMs, and their 'recombinant' technology is a rubber cap held in place by the lid which can easily be pried off.
I think they have issues overheating once they've aged and require more and more amperage to be held at float, and perhaps have been floated too high for too long, at the occasionally too high an ambient temperature, while within their ergonomic enclosure.
I accept the potential age issues with these, and insure I hold absorption voltage as long as is required for amps to either stop tapering, or taper to 0.5% At 14.7v, indicating full charge. After this i discharge to 50% or more notine rate and voltage retained, then see how much it wants to feed upon at 14.7, when allowed 40 amps.
That MAX charge rate recommendation is a CYA statement, in my opinion. use common sense, and keep em from getting too hot.
My new 22 Ah AGM says 'NO amperage limit', with a 13.6 to 13.8v charging source in 'standby duty' but does say a 6.6 amp maximum at 14.6 to 14.8v in 'cyclic' duty.
Whereas they use to say only half the rateat 13.6vcompared to 14.7v. Obviously higher pressure , more amps flow, but hook a huge charging source set at 13.6v to 13.8v to a well depleted agm, and the first few minutes will accept huge amperages well over that 'recommended' maximum amperage rate, before the delta narrows and less amps flow.
Floating at proper temp compensated voltage(13.6ish@77f) for an additional 12 hours might have amps taper to near zero and quickly decline to near there when voltage is boosted back upto 14.7v, but sometimes amps at 14.7v never tapered to 0.5% of capacity with these but seems to get better with some cycles accumulated.
Really, these cheap Asian AGMs might be great, or lackluster, depending on your requirements and expectations and ability to attempt to recharge completely, on occassion.
In the bigger sizes, the Deka Intimidator AGM, perhaps relabelled by sams or costco or autoparts stores, can be had for similar prices, and at least is USA made.
Take your digital voltmeter and buy fresh,
but 'click order' of these UPG/ UB asian AGMS and you have no choice with the age of battery which arrives.
Good luck
