in essence, since you are doubling the output of a 12v 220amp hour SERIES battery 'bank', when in PARALLEL with another, you are then doubling the amp hours to 440.
Use 400 if that is your only option - it's close enough for hand grenades, horse shoes, and submarines. (...that's a good 'ol saying from another time!)
Series(Positive to Negative) wiring doubles the VOLTS, but thereby decreases the HOURS
Parallel(Positive to Positive) wiring doubles the HOURS, while maintaining the same VOLTS
here's a photo of my house battery bank:
DURACELL GC(GolfCart) 6v 215ah Battery bank...
in Series and Parallel = 12v at 430ah = 215ah usable power for
FLA Flooded Lead Acid batteries
two Campers, two Electric cars
former diesel pusher traveler