Sterling Power Saturn BB123665 | 12V/24V to 36V 850W Bidirectional DC-DC Battery Charger

The BB123665 is Sterling Power's Saturn Series DC-DC charger for 36V lithium and lead-acid battery systems — a purpose-built solution for overlanders, van builders, and expedition rigs running a 36V house bank charged from a 12V or 24V alternator. With 850W of continuous output and Sterling's proven Saturn platform, it handles the voltage step-up cleanly while protecting both your alternator and your batteries.

Like all Saturn Series chargers, the BB123665 auto-detects whether it's connected to a 12V or 24V source — no configuration needed when switching between vehicles or power sources. It's fully compatible with Euro 5/6+ smart alternators that use variable voltage regulation, making it the correct choice for any modern vehicle where a traditional relay or older-style charger would cause alternator faults or fail to charge at all.

The BB123665 delivers a proper 4-stage charge profile (bulk, absorption, float, and equalization for lead-acid) with six preset battery type profiles covering gel, AGM, calcium, open lead-acid, and two lithium profiles. Low-temperature lithium cutoff protects LiFePO4 cells from charging damage in cold conditions. At 96% efficiency, very little energy is lost as heat, and the unit runs a thermostatically controlled variable-speed fan that only spins up under load — quiet at rest, active when it matters.

Bidirectional Reverse Charging: When your 36V house bank climbs above threshold, the BB123665 automatically feeds current back to your 12V or 24V starter battery to maintain it at a healthy float voltage — so if solar is looking after the house bank while the rig sits, your starter is looked after too. If the starter ever drops too low to turn the engine over, Jump Start Assist mode forces the reverse charge to run for 20 minutes to get you back in action.

Output can be set to 100%, 85%, or 65% via the optional BBR remote — useful for dialing back alternator draw when solar is contributing, or when running multiple BB units in parallel for additional capacity or redundancy.

Specifications

• Model: BB123665
• Input Voltage: 12V / 24V auto-select
• Output Voltage: 36V
• Continuous Output: 850W
• Efficiency: 96%
• Cooling: Thermostatically controlled variable-speed fan
• Dimensions: 200 x 130 x 56mm
• Weight: 1kg
• Smart Alternator Compatible: Yes (Euro 5/6+)
• Bidirectional: Yes — reverse charge + Jump Start Assist
• Remote: Optional BBR remote for output adjustment