The Bendix King Battery Eliminator, BADPHBE9R - with Cigarette Lighter Plug is designed to work on a 12 volt DC system. In order to use the battery eliminator on a 28 volt system there would have to be a power converter installed at the cigarette lighter plug to reduce the voltage to 12 volts.
Customer Support at BendixKingRadios.com answered on October 6, 2017
Just plug this into the plug in my water tender and I don't have to worry about charging anymore. I carry clamshells for when I have to leave the truck. If you are working mostly from a vehicle this is a great product. (Posted on 6/2/2016)