STINGER SGP35 12V High-Current 500A Relay Dual-Battery Isolator — Water-Resistant, 900A Surge

The STINGER SGP35 is a water-resistant, high-current 12V relay that isolates a secondary battery and safely transfers up to 500A continuous (900A surge) while your vehicle is running.

Designed for car audio systems, auxiliary power packs, and demanding electrical setups, the SGP35 relay allows a second battery to charge only when the ignition is on, preventing unwanted drain on the main starter battery. Built in a durable phenolic plastic housing and rated for 100,000 mechanical cycles, this isolator delivers reliable switching in marine, powersports, off-road, and automotive environments. It works with any alternator or charging architecture and provides a compact way to add a dedicated battery for electronics without compromising starting power.

How does this relay keep my starting battery from losing charge?

The SGP35 stays open when the ignition is off, keeping the auxiliary battery electrically separate so accessories cannot draw from the starter battery. When you turn the ignition on, the relay closes and allows the alternator to charge both batteries, then reopens after shutdown. This automatic behavior removes the need for manual switching and reduces the risk of a dead starter battery.

• Automatic ignition-activated switching—no manual toggles required
• Keeps batteries isolated when vehicle is parked
• Compatible with single or multi-output alternators
• Prevents accessory drain on primary starting battery

What are the electrical capabilities and durability of the SGP35?

The SGP35 is engineered for high-current environments: it handles 500 amps of continuous current and tolerates surge currents up to 900 amps. The contact design and materials target longevity, with a rated mechanical life of 100,000 cycles. Housings made from water-resistant phenolic plastic protect internal components from moisture and abrasion in harsh settings.

• 500A continuous current rating with 900A surge tolerance
• 100,000 mechanical cycle life for long-term reliability
• Water-resistant phenolic case for marine and off-road use
• Suitable for heavy audio amplifiers, winches, and multi-battery systems

How simple is installation and what vehicles does it support?

Installation is straightforward: mount the relay in a protected location, wire the battery and alternator connections, and add an ignition-switched trigger. The unit’s universal 12V design means it works with virtually any vehicle alternator or charging system, from standard cars to boats and off-road rigs. Use appropriately sized cables and fusing to match your system’s current demands.

• Mounts with basic hand tools in a secured spot
• Ignition-switched trigger wire activates the relay when running
• Works with all types of 12V alternators and charging systems
• Requires heavy-gauge battery cables and proper inline fuses

Will this relay work with my car audio or accessory setup?

The SGP35 is ideal for powering high-draw accessories—like amplifiers, fridges, or lighting—using a dedicated auxiliary battery that won’t compromise engine starting. By isolating the batteries, you get a stable power source for audio systems and electronics while maintaining safe starting power. It pairs well with multi-battery installations and aftermarket charging upgrades.

• Provides a dedicated power source for amplifiers and accessories
• Prevents audio or accessory usage from draining the starter battery
• Compatible with dual-battery configurations and charging upgrades
• Robust enough for continuous high-power draws during operation

Who is this for: The STINGER SGP35 suits car audio enthusiasts, overlanders, marine and powersports owners, and anyone adding a secondary battery for high-draw accessories. If you need a compact, reliable isolator that handles heavy currents, resists moisture, and automates battery management without altering your alternator, the SGP35 is a practical choice.