Time to charge a bank of 8 6v batteries using a generator

"So a 65 amp charger can draw about 900 watts from the generator for the first hour, and less each additional hour. You could run two of them on a Honda 2000, as they will start out a little above the 1,600 watt rating, but will fall within the max range within 45 minutes or so."

If that were true, I'd be doing it.

Generators are at least 10X the cost of a battery, and yet many folks are so concerned with getting an extra year or so out of their batteries, they gladly blow thru an extra gennie to do so?