thats a total of close to 440 amp hours. If you deplete them all the way down and wanted to fast charge them at about 100 amps (max 50 amps per battery) even with the engine running it might take several days. You can get it to 60 percent in about 4 hours then the absorb phase will take 10 hours are longer. The battery will only accept 100 amps when its empty as it gets full it accept less amps, in other words you can't rush them. But you only have to fully charge them once in a while to keep the agm healthy, the rest of the time just get it as close to full and continue using them.
Solar on the other hand, will never fully charge 440 amp hour batteries. I have a 240 watt panel and a 94 ah lithium battery and fully charge it should read 12.6 volts, in winter it never get up there, mostly 12.1 is the highest I see, it spends all day in absorb mode. With 240 watts and mppt I get 9 amps in winter and 12 amps in summer. Solar is all I use and even in winter I can go several days with cloudy/rainy weather and my lithium battery wont get under 40 percent. In your situation you would need at least 2 large panels with an mppt controller to at least provide you usable power. A 100 watt panel (5 amps) or smaller will only be trickle charging such large batteries, even I wouldnt use something so small to charge my 94 ah battery. Trickle charging is ok if the batteries are already full,but agms like high amps to charge them.
I would definitely recommend solar if you got the room, once fully charged, the solar will keep your batteries topped off and save you gas in the long run. If your power use is minimal, you might never have to run your generator except maybe once a month to give the battery a good high amp charge for battery health purposes. With agm batteries undercharging them constantly will kill them.
