According to the specs the Eva-Dry 1100 uses 22.5 watts of power, which would be a bit over 1.8 amps @ 12v. Apparently that is not continuous and it uses that power when its "renews' itself, a process that apparently take 10-12 hours but does not happen every day. I have no idea how long it would take to flatten the batteries - it depends on how often it "renews" itself. But one renewal cycle of 12 hours for two devices would probably flatten one 12v battery.
Does the 1100 use 12v to renew or is it like the smaller ones that plug into a wall outlet?
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL