I hate generators enough that I don't have one, but my rig is just a DIY class B and built around my specific needs and if I wanted/needed one I would have to device some new way of carrying it, so I'd rather not need it.
Reaching Absorption at the battery terminals ASAP, is how fastest possible recharging is accomplished.
The battery acceptance ability itself plays a huge part in this, and the health of the battery(s) is a big part of how much amperage it takes to instantly reach absorption voltage, and for how long it can accept high amperage while it tapers towards full.
Health of the battery is directly related to how often it has been brought back to 100% state of charge, however quickly.
Generator charging, Max SOC% reached in minimum time is about a high amp charging source which can quickly bring the battery to its temperature compensated absorption voltage. I call it quench charging, and My Specific 103AH AGM-31 battery seems to love it.
Its only a few months old, but 134 amps was recently not enough to instantly bring it to 14.7v from ~ 40% state of charge, and I tripped a circuit breaker and slightly melted the head of a 12 awg 25' extension cord in the process. I had to settle for a 'peasly' 94 amps afterwards which then took a few more minutes before hitting 14.7 at which point amps tapered, and pretty quickly tapered.
I'll be adding a second separately regulated alternator( i use a manual adjustable external voltage regulators in the not too distant future, its the only way I will be able to establish what 'Quench amperage' is on this battery as a 94 and a 40 amp charging sources in parallel, are not enough.
A well depleted 18Ah chinese AGM battery(UPG UB`12180) spiked at 38.3 amps and 5 seconds later was accepting 32 amps@14.7v and 5 minutes later 25 amps.
One of the boat guys found that charging an AGM to full, with huge amperage sources only cut 12 or 20 minutes off the total ~5.5 hour time to reach true 100% SOC, but huge recharging amperages for shorter periods were able to achieve much higher states of charge, and its always better to begin the next discharge from as high a state of charge as possible. If achieved early in the day, and if one has solar to finish off the process, can equate to happy long lived daily deep cycling lead acid batteries.
https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/I don't know the current Powermax adjustable voltage lineup like BFL-13 does, but one of these with short fat cables to battery which maxes out the generator's ability for the elevation, is how to achieve as high a state of charge as possible in minimum amount of generator run time.
POwerfactor correction comes into it. The PD9280 requires a 20 amp receptacle whereas the 100 amp PFC powermax can run on a 15 amp outlet, but maxes it out, or nearly so.
My mains charger is a modified Meanwell rsp-500-15 which is PFC, capable of 40 amps at any DC voltage between 13.11 and 19.23v, the 100 amp adjustable voltage Powermax I have in my workshop which maxes out at 94 amps and as high as 15.5v under lighter loads, is not exactly mine, and is an older model no longer offered.
I've got a 50 amp 'Ideal diode' on the Meanwell's output, which only drops 0.04v at 40 amps.
I'm considering getting another MW, as it will fit my available space easily, where the Powermax never could, and 'quench amperage' is outside my ability to attain via plug in charger anyway.
I used to parallel my MW with a 25 amp Schumacher 'smart' charger without the Diode, without issue, and I've been using the modified MW since September 2014 as my main charger/ converter/floater/portable charging source, and its got thousands of hours on it and I credit it to the exceptional lifespan of my Previous AGM battery, and really any battery I have been tasked with keeping alive for as long as possible.