Tiffin Breeze as well as all current Tiffin models use a Trickle type Battery Maintainer for the chassis batteries. That means IF your chassis batteries are completely dead, that Small Maintainer cannot charge completely dead batteries. So, using the Battery Boost switch, hold it down or use a toothpick to keep it engaged for at least 1 to 2 hours while plugged into Shore power. That will allow the Coach Battery charger to charge the chassis enough to let the Maintainer start up and then fully charge the chassis batteries. It will take a week or so. I would leave the Toothpick in the Battery boost switch for 24 hours and then remove it. The chassis Batteries will almost be fully charged by then. Doug