I have an 18Ah AGM, the UB12180, though the one I have is marketed towards the stereo boom boom crowd, and is called a '600 watt' battery. I suspect it is just the UB12180 with a different sticker.
Anyway, I have depleted this battery to well below 50%, and hooked it to my 40 amp power supply, set at 14.7v.
Peak amperage was 36, to raise voltage that high instantly. This quickly fell to 32 amps and about 5 minutes later it was still accepting 25 amps at 14.7v.
Max charge rate listed for the UB12180 is 5.4 amps!
No mushroom cloud exceeding that rate by several fold.
The 25 amps was holding steady when I could not be around to monitor battery temperature, so I lowered voltage until only ~ 10 amps were flowing, and then raised it back up on subsequent passes back upto 14.7v and held it there until amps stopped tapering.
Even 10 amps is well above the 'max' 5.4 amp charging rate.
No mushroom cloud.
This battery has, by itself started my 2 week cold 5.2 liter v8 engine in warm ambient temperatures. My dual wattmeters inline on the dual 8awg cable recorded close to 1800 watts of draw on the battery with their peak watts added together.
No mushroom cloud.
This battery in parallel with my fully charged regular group 27 AGM battery, will provide 50 amps assist, when starting the motor over a single pair of 8awg wires. This number varies depending on the state of charge of the 27.
No mushroom cloud.
Obviously, I would not be discharging this thing to below 50% at huge discharge rates on a regular basis, nor regularly exceeding its max recommended charge rate by a factor of 6 on a regular basis, but some seem to think that the mushroom cloud is just around the corner if it sees either too high a charge or discharge rate once.
I'd not be searching for any product to keep the generator battery healthy, I'd occassionally parallel it with the regular batteries when they are being held at absorption voltages, bring it to ~14.7v for a few hours each week. This can be as simple as whatever length of 18AWg lamp wire you can salvage, hooked to the battery and a ciggy plug.
These chinese AGMS do not have super low self discharge like higher quality AGMs, but they don't need a constant trickle charge either in my opinion, especialy one that does not consider battery temperature and vary voltage accordingly.
If thee small chinese AGMS are unintentionally deeply discharged, I would feed them no less than 30% of their rated capacity upto their absorption voltage, and the UB/UPG batteries list a 14.5 to 14.9v absorption voltage in 'cylic' duty. If you look at the UPG or UB battery spec sheets the max rate is always 30% of their capacity.
There are loads of DC voltage boosters online. I got a 150 watt one for less than 3$ shipped slow boat from china. So far all I have used it for is making 12v fans levitate at 27 volts, but I would have little issue using it to EQ a battery or as a inline voltage booster for too thin and too long of wire feeding a distant battery.
