First: The ADVERTISED capacity is not the ACTUAL output of most chargers. The internal heat load of the charger circuits often reduces the actual output. I don't know if this is the case with the units that you are considering; however: Our 200 Amp Mastervolt produces about 135 Amps of real maximum capacity after it "heats up" a few minutes after starting. Our prior Xantex (a/k/a Heart) 130 Amp charger never put out 60 Amps in the real world.

Secondly, I've found, with various loads running, the effective charging output is diminished by the "background" current load. If you have other items on a 12v circuit -- say 25-30 amps with a computer, refrigeration, water pump, lights, etc. -- then the charger's actual through-put to the batteries will be diminished by that "draw-down" before it goes to the batteries.

You're bank will unlikely like not being able to be topped-out by a little current in terms of sulfation. If you had a power interruption, then you really won't be charging the batteries up very quickly, in any event.

So, I'd get the biggest battery charger you can. If the "real world" output is 60-70% of advertised output, and you want to be able to charge your battery bank at 15-20% of the amp-hour total, the my approach would be to have 480 amp hours x 20% / 70% = 130 amps. Since you only want this a supplemental charger, I wouldn't go below the 40 amps if your choice is that.

By the way, are you sure that the rating in output at 220 volts doesn't go higher than 40 amps?