Dual Battery Setup - DC-DC Isolator (Blue Sea / Redarc)
Add a second battery isolated by a voltage-sensitive relay (Blue Sea ML-ACR) or DC-DC charger (Redarc BCDC1225D) to run a fridge, lights, and winch without killing your starting battery.
For overlanding, dual batteries are the standard. The two main approaches: (1) a voltage-sensitive relay/ACR like the Blue Sea ML-ACR 7622 which automatically combines the batteries when voltage exceeds ~13.6V (engine running) and isolates them below ~12.75V — straightforward, around $200; (2) a DC-DC charger like the Redarc BCDC1225D which actively boosts the alternator output to fully charge an AGM aux battery and includes MPPT solar input — $400-500 but the only way to properly charge a lithium aux from a small alternator.
Wire heavy gauge (2 AWG minimum, 1/0 preferred) from main battery+ through fuse, to ACR/DCDC, to aux battery+. Each battery needs its own MEGA or ANL fuse within 12 inches of the post. Mount the ACR/DCDC on a vertical surface for heat dissipation.
The Blue Sea ML-ACR adds a manual override switch for emergency jump-starting from the aux battery. The Redarc BCDC adds a Start Isolate input that should be wired to switched ignition so it doesn't try to charge from a dying battery during start.
Why it works
- protects starting battery
- DC-DC works with lithium
- automatic operation
Trade-offs
- expensive vs solenoid
- needs space for second battery
Tools required
- crimper
- drill
- step bit
- wire strippers
- multimeter
Parts
| Part | Vendor | Est. price |
|---|---|---|
| Blue Sea ML-ACR 7622 | Blue Sea Systems | ~$200 |
| Redarc BCDC1225D DC-DC charger | Redarc | ~$450 |
| Blue Sea MRBF terminal fuse 100A (x2) | Blue Sea Systems | ~$40 |
| 2 AWG cable kit | WindyNation | ~$80 |
Sources
Related
- Dual Battery Setup - Continuous-Duty Solenoid
- Second Battery Tray Relocation (Cargo Area / Rear)
- All Jeep Cherokee XJ guides & tools
- Browse the full DIY database
Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.