I use a dcdc in my Pajero because of the smart alternator and 2 x 130 amp agms in the rear tub. I have another in the camper...both fed from the one cable via fuses. Been excellent for 3 years now. Ford Ranger also say in the handbook that a dcdc charger is the best method to use for an aux battery set up. (According to a post on a forum from a bloke who owned a new ranger and asked for a please explain. ). Redarc now produce a 50amp dcdc charger and I,d expect others will have more powerful ones to come.