I can't imagine running a Genny to charge 2 27s at 6 amps total.
Max that Honda out with the products recommended. The 27's will be much happier despite grandpa's oft repeated 'trickle" charge always being best, which has been handed down through the generations.
I see this often on other forums. Someone will kill their battery and somebody else says to put it on a 2 amp trickle charger overnight, not aware that the ~24 amp hours returned might only be 1/3 or less the total capacity of the battery.
It might be enough to allow the car to start though. Poor abused batteries cant catch a break from the ignorance of the motoring public.