Premium Quality: The voltage sensitive load relay is made of fiberglass reinforced nylon, sturdy and durable. It does not age easily and resists abrasion, ensures maximum strength and durability for long-lasting use. 125 Amp Dual Battery Isolator Smart Isolator: The voltage sensitive relay of the dual battery isolator is all you need to charge battery systems. Its dimensions fit the heavy-duty modular fuse boxes (BF43X) and battery switches, which correspond to common products on the market. Ideal for dual battery vehicles: the relay kit 125 Amp 12V Voltage Sensitive (VSR) Split Charging is the best way to ensure you can always start your dual battery vehicle. Once your primary starter battery has sufficient charge, it will begin charging the second battery. Easy Installation: The 12V VSR Voltage Sensitive Relay with surface or wall mount options panel, which provides flexibility during installation. No voltage loss compared to battery isolator diodes (0.6V). Combined / open voltage: 13.3 V / 12.8 V DC.