I have an 18 amp hour, 11.1 LB mightmax AGM battery. Marketed to the stereo boom boom cowd as a '600 watt' battery
I am not convinced it is any different than the generic UPG/UB12180.
MM did tell me to use the charging specs for the Ub12180 when I asked.
When this battery was new, It was ( just barely) able to start my 2 week cold, 5.2 liter v8 engine, by itself, in warm ambeint temperatures
It was close to 1800 watts of load, from a 1.4KW( output) starter. Voltage dropped to the mid 7s
1800 watts divided by 7.5 volts is 240 amps.
Nowhere gives a CCA spec for this battery, I estimate it is around 160 to 180.
It is 2+ years old now. I kind of doubt it could start the v8 at this point, despite keeping it fully charged between uses
for a 35$ battery, I have gotten my money's worth from it, and it is not dead yet.
I drained it to 7.66v under an average ~ 4 amp load applied for 2.5 hours last night, then charged it on a 40 amp adjustable voltage power supply set to 14.7v.
It peaked at 35 amps, then held steady accepting 30 amps for much longer than expected.
i was monitoring temperature rise closely, and one cell in the middle was heating more significantly than the others. i lowered voltage until only 20 amps was flowing and within 25 more minutes hour it was accepting under 5.4 amps, its supposed max charging rate.
The battery had gone from 71f to 94f. during this charge rate which exceeded the maximum listed on the PDF above by a factor of 4 to 6.
At that point I lowered voltage to 13.6v and went to bed. Some 12 hours later it was accepting 0.05 amps @13.6v, and when I boosted voltage to 14.7 iamps rose to 0.47, then dropped to 0.32 in about 15 minutes, then started rising again at which point I removed it from the charging source.
The YTZ12s is about the same size and weight as the UB12120, but it is hard to find a UB12120 with T3 terminals, not the common f1 or f2 on this size battery.
I had a Ub12120 in a schumacher mitymite jump box, with the fatter T3 terminals, and it was a capable jumpstarter, but I just used it for parts rather than replacing the battery within when it could not longer jumpstart an engine with a weak main battery.
All lead acid batteries Flooded/AGM/GEL, ideally want to be truly fully charged held up at high states of charge, and never overdischarged and not exposed to hot temperatures. A long slow parasitic drain to low states of charge, followed by an incomplete recharge, will quickly degrade any battery, no matter its price point.
If you can find a cheapo AGM battery which fits and has acceptable terminals to easily attach to your bike, get yourself some sort of charging source which can bring it upto 14.5 to 14.9v, until amps taper to very low levels or start rising, then disconnect the parasitic loads if the bike is to sit, recharge monthly, at a minimum, and you can likely get good to excellent service from it.
