Mastervolt Mac Plus 12/48-15 [81203205]Mac Plus 12 48 15 Boost Your Service Battery Too often, service batteries dont get the charge they need. This is a problem made worse by smart alternators and start stop systems, which result in slow and insufficient charges. The Mac Plus 48V and 36V solve that problem. With brand new bi directional technology, the Mac Plus can use each side as an input or output, delivering a reliable and consistent charge to both service and starter batteries.