Eliminates the inconvenience and danger of unbolting your battery cables. Once installed, simply rotate a switch to disconnect your battery. Because it is heavy-duty, you can use this kit on diesels and other vehicles with high cold cranking amps. The Battery Disconnect also has other applications, such as a hidden kill switch to deter auto thieves. In some cases, a vehicle will have two batteries. If BOTH batteries are on an engine starting circuit you will need one for each battery. If only one of the batteries is used on the engine starting circuit then only one battery disconnect is needed. Many late model vehicles must have their battery disconnected for dinghy towing. Failure to do so will lead to a dead battery. Even with the battery disconnected, some dinghy accessories (such as braking systems and breakaway kits) require power while the vehicle is in tow. The accommodates this by providing a positive current source even when the battery is disconnected. If you are unsure if your vehicle drains the battery while towing.