The Sterling Power BB123665 is a 12V/24V-to-36V DC-DC (battery-to-battery) charger from the Saturn range. It automatically accepts a 12V or 24V input and steps it up to deliver a controlled, multi-stage charge to a 36V battery bank – ideal for 36V lithium or lead-acid systems in overland, marine, and specialist builds. If you are new to dual-battery systems, the principle is straightforward: you cannot correctly charge a 36V bank straight from a 12V or 24V vehicle supply, and lithium in particular needs a controlled charge. The BB123665 does exactly that. Rather than a simple converter, it measures both current and voltage and steps intelligently through bulk, absorption, and float, giving your 36V bank a full, correct charge. It is bidirectional and lithium-safe, rated at 850W with 96% efficiency. Charging Specifications Type 12V/24V → 36V bidirectional battery-to-battery (DC-DC) charger, Saturn series Input voltage 12V / 24V autoselect Input voltage range Available on the datasheet – contact us to confirm Nominal output voltage 36V Max output power 850W Max output current Available on the datasheet – contact us to confirm Max input current Available on the datasheet – contact us to confirm Efficiency 96% Reverse / jump-start current Bidirectional reverse-charge + jump-start assist – exact current available on the datasheet; contact us to confirm Battery profiles 6 selectable (Lead, AGM, Lithium) + custom via optional BBR remote Temperature sensor Included Cooling Thermostatically controlled variable-speed fan Protections Self-recovering: under-voltage, input & output over-voltage, over-current, over-temperature Recommended cable / fuse Available on the datasheet – contact us to confirm Dimensions 200 × 130 × 56 mm Weight 1.0 kg Operating temperature −20°C to +60°C Certifications CE, UKCA Warranty 5-year return-to-factory Key Features Steps a 12V or 24V vehicle supply up to a controlled, multi-stage 36V charge – input auto-selected 850W continuous output at 96% efficiency using buck-boost technology Lithium-safe with 6 selectable battery profiles (lithium, AGM, and lead) plus custom profiles via the optional BBR remote Bidirectional reverse-charge and jump-start assistance Smart-alternator / Euro 6+ compatible with included temperature sensor Self-recovering protections; CE / UKCA approved; 5-year return-to-factory warranty Smart Alternator / Euro-6 Ready Three engagement modes cover any vehicle: automatic voltage sense (engages once the alternator is charging), ignition-feed control (for smart / Euro-6 alternators), and vibration sense (begins charging once the internal accelerometer detects the engine running – no ignition wire required). Installation Notes Use a common, direct negative between the source battery, charger, and 36V bank. Take the positive input from a circuit fed by the starter battery (or an Alternator Linearisation Device) – not straight off a bare alternator. Rate the charger to no more than about 80% of your alternator's output. Fuse both the input and the output, and size cable and fuses to the current rating on Sterling's datasheet for your run length – contact us and we will confirm the exact figures for the BB123665.
