Considering my fishfinder goes portable in the winter with a 9 ah and it lasts all day
a 27 group 100 amp battery will have no problem with 2 graphs
i ran a HDS 8 on a single battery for a week 12 hours a day fishing from a 14 ft boat with no charging system and no power at the cabin and it lasted so there is a problem with his battery or system
Something is draining his battery or the battery has issues