Smart Dual Battery 140A Isolator (VSR Voltage Sensitive Relay) for Auto/Boat/RV 12V 140A smart isolator with Cut-In:13.4V, Cut-Out:12.9V Easy 3 wire connection at the battery. No need to bypass existing alternator wiring The smart isolator has no voltage drop. Conventional diode isolators incur a minimum of 0.6 volt drop Compact 2.5 inch by 2.5 inch by 2 inch size - No large heat sink Easy to install anywhere - Water and dust resistant