Two batteries No problem! The Charge Mate series connects both batteries during charging and keeps them isolated when discharging. The Charge Mate Pro 40 provides additional functionality by limiting the charge current to the second battery to 40 Amps, so the main battery is charged with priority. The return current is automatically blocked, which reduces power dips of the onboard network. An emergency-start function is possible by connecting an optional bypass switch.Details:Electronic charge coupling with very low voltage dropCharge current secondary battery limited to 40 AmpsHigh system reliability by prioritized charging of the main batteryUnidirectional; blocks return current under all circumstances, which reduces power dips of the onboard networkSuitable for all kinds of battery chargers and alternatorsLED status indicationIP67 electronics in a corrosion-resistant casing with aluminum heat sink