This unit is perfect for keeping your campervan's starter battery topped up by transferring excess power from the leisure battery, which is especially useful when solar panels are charging the leisure battery. Once your leisure battery reaches about 13.3V, the unit activates, allowing surplus energy to flow to maintain the starter battery. While it doesn't offer fast charging or boosting, it mirrors the input voltage with only a small drop (typically around 0.2V less than the primary charge), which is more than sufficient to keep the starter battery topped up and cover small loads like the battery's internal discharge and the engine management system (up to 1A continuous). This feature is invaluable during periods of non-use, ensuring your starter battery stays healthy without the need for external charging. This unit is the perfect substitute for a dual-output solar charge controller. Instead of needing a solar controller with dual outputs to manage both your leisure and starter batteries, this unit simplifies the process by allowing excess power from the leisure battery to maintain the starter battery. With solar panels continuously topping up the leisure battery, this device efficiently manages the distribution of surplus energy, ensuring both batteries stay charged without the need for more complex or expensive equipment. It's an ideal solution for those looking to streamline their campervan's electrical system while keeping both batteries in good condition. Victron Dual Output MPPT Solar Charge Controller - It doesn't exist but this is the perfect alternative!