Sterling Power BB1248120 12V/24V to 48V 120A Bidirectional DC-DC Battery Charger

The Sterling Power BB1248120 is the high-output Saturn series charger for builds running 48V house battery systems — think large LiFePO4 rack batteries, high-capacity inverter setups, or any serious off-grid electrical system that has moved to 48V for the efficiency and wiring advantages it brings. It takes alternator power from a 12V or 24V starting system and delivers a fully regulated, 4-stage charge to your 48V house bank at up to 28A output and 1,500W of continuous charging power — double the output of the BB124865 in the same form factor.

The unit auto-detects whether your input is 12V or 24V — drawing approximately 120A from a 12V source or 60A from a 24V source — and configures itself accordingly. For builders running 16S LiFePO4 rack batteries at 51.2V, the BB1248120 handles that application natively at full power. Running a 15S Pylontech or similar battery requiring a lower absorption voltage? The optional BBR remote allows full custom charge profile programming down to the specific voltage your cells need.

Like every Saturn series unit, the BB1248120 applies the correct charge algorithm for your battery chemistry across six preset profiles covering Lead I and II, AGM I and II, and Lithium I and II. A low-temperature cutoff protects lithium cells in freezing conditions, and six self-recovering protection circuits manage over-voltage, under-voltage, over-current, and over-temperature faults without manual intervention. We recommend pairing this unit with an alternator rated at least 20% above the 120A input demand to protect your charging system under sustained load.

Bidirectional reverse charging is standard. When your 48V house bank climbs above 52.8V (54.0V on lithium profiles), the BB1248120 automatically feeds up to 40A back to the 12V starter battery (or 20A to a 24V starter) to maintain it at a healthy maintenance voltage — so if solar is looking after your house bank while the rig sits, your starter is looked after too. If the starter ever gets 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.

The BB1248120 is fully parallelable with other Saturn series units for expanded output, and supports the optional BBR remote for live monitoring, custom charge profile programming, and output current limiting from anywhere in the vehicle.

Key Specs:

• Input voltage range: 9–16V (12V) / 18–32V (24V) — auto-detecting
• Rated input current: 120A (12V input) / 60A (24V input)
• Rated output: 28A at 57.6V (~1,500W continuous)
• Reverse charge current: 40A to 13.4V (12V) / 20A to 26.8V (24V)
• Efficiency: 92–94%
• Dimensions: 270mm × 130mm × 73mm
• Weight: 1.8 kg
• Recommended input cable: 35mm² / 2AWG
• Recommended input fuse: 150A
• Recommended output cable: 6mm² / 10AWG
• Recommended output fuse: 40A
• Certifications: CE, UKCA, E-Mark
• Cooling: thermostatically controlled variable-speed fan
• Compatible: lead acid (AGM, gel, flooded), lithium LiFePO4 (16S and 15S with BBR)

Compatible with smart/variable alternators (Euro 6/7+). Ignition feed or vibration sense activation modes. Optional BBR remote available for display monitoring, custom charge voltage adjustment, and output current limiting.