A REDARC Smart Start SBI connects and separates two battery banks according to voltage. It is a switching isolator, not a DC-to-DC charger or solar regulator. The SBI12 is a 12V, 100A unit that monitors the start-battery side; the SBI12D adds dual sensing for charging from either bank; and the SBI212 is a heavier-duty 200A version. The factory diagrams identify the high-current studs and the optional blue-wire override.
Compare Smart Start SBI battery isolators
| REDARC part | Continuous current | Voltage and sensing | System function |
|---|---|---|---|
| SBI12 | 100A | 12V; start-battery sensing | Connects auxiliary battery when the start battery is charging |
| SBI12D | 100A | 12V; dual sensing | Connects when either bank is being charged |
| SBI212 | 200A | 12V; start-battery sensing | Larger isolator for higher-current systems |
| FK60 | 60A MIDI fuse kit | For appropriate SBI12 installations without the start-assist override | Observe manual's circuit-dependent fuse sizing |
Identify the factory wiring connections
| Drawing location | Function | Check when installing |
|---|---|---|
| Start battery stud | High-current connection to the starter battery | Must have correct battery-end fuse or breaker |
| Auxiliary battery stud | High-current connection to the second battery or loads | Fuse or breaker close to the auxiliary battery |
| BLACK wire | Common chassis ground lead | Correct contact is needed for voltage sensing |
| BLUE wire | Optional indicator LED or momentary start-assist override | Do not connect directly to the unit's internal control terminals |
| 100A SBI12/SBI12D | 13.2V turn-on; 12.6V turn-off nominal thresholds | 100A continuous rating; momentary 400A inrush |
| 200A SBI212 | 13.2V turn-on; 12.6V turn-off nominal thresholds | 200A continuous; different housing and cable/fuse sizing |
| SBI12D dual sense | Observes both banks when alternator or auxiliary-bank charger is active | Useful when regulated solar charging is connected to the auxiliary side |
| Separate solar regulator | Converts panel output into suitable battery charging voltage | An SBI12D does not replace a solar charge controller |
| Override enabled | 100A unit may require 100A MEGA protection; consult length chart | REDARC specifies different sizing with and without override |
| Status LED | Illuminates when the contacts combine the batteries | Flashing sequences indicate manufacturer-defined faults |
Original REDARC wiring and terminal diagrams
The factory illustrations identify the cables, fuses, terminals and charging connections for the specified model family. Open them at full size when installing or servicing equipment.
REDARC standard SBI12 battery-isolator wiring and override connections
REDARC SBI12D dual-sensing solar charge and auxiliary-battery wiring
Open the REDARC SBI12D dual-sensing wiring diagram (PDF page 5)
Charging method and cable protection matter
Unlike a DC-DC charger, the SBI12 does not apply a programmable battery profile or boost/regulate charging voltage. The factory manual recommends compatible lead-acid battery types and appropriate fusing close to both battery terminals. The SBI12D allows charge to flow from either battery bank when its voltage criteria are met; use an independently regulated solar source. A 200A SBI212 is not a direct swap into 100A wiring without reviewing terminals, cable gauge and circuit protection. Use the REDARC schematic and a qualified installer.
Related RV battery-system references
Battery isolators and related accessories
Select a photo to open its NewRVParts listing. Similar-looking components may have different current limits, terminals or fitment.
SBI12 — REDARC 12V 100A Smart Start Battery IsolatorSingle sensing; start-battery priority
SBI12D — REDARC 12V 100A Dual-Sensing Battery IsolatorDual sensing for charging from either battery bank
SBI212 — REDARC 12V 200A Smart Start Battery Isolator200A version; different stud and protection sizing
FK60 — REDARC 60A MIDI Fuse Kit60A protection recommended for Classic40/50
SBI12 — REDARC 12V 100A Smart Start Battery IsolatorSingle sensing; start-battery priority
SBI12D — REDARC 12V 100A Dual-Sensing Battery IsolatorDual sensing for charging from either battery bank