Some good tips to pass along.. By: PB Editor Wednesday, July 3, 2013 Roy Hellmund, engineering and technical specialist for Interstate Batteries, provides the following information on checking for voltage drops that can adversely affect engine performance: One thing that is commonly overlooked when it comes to the charging system is the potential to have voltage drops affect the operation. A simple voltage drop test can let you know if you have problems or need to upgrade the positive cable. This is how the basic voltage drop test would be performed: Set the parking brake and block the drive wheels, start the engine and turn on as many electrical accessories as you can to load the alternator. Using a digital DC voltmeter, connect the positive lead to the output stud of the alternator and the negative lead to the positive battery post. The reading indicates the voltage loss through the resistance of the cable and connections on the positive side. Now, move the positive lead to the alternator case and the negative lead to the negative battery post. The reading indicates the voltage loss on the negative side of the circuit. Don’t worry if the voltmeter reading is negative; just treat it like a positive number and add the positive side and negative side voltage drops together to get the total. Generally, the total maximum voltage drop for the alternator should be no more than 0.1 to 0.2 volts. Positive-side drops can be addressed by cleaning and tightening connections or replacing the positive cable with a heavier gauge size. Negative side drops can be addressed by cleaning the alternator mounting surfaces and battery cables. The voltage drop test should also be used to test the battery cables for any issues. Test the positive then the negative side while cranking the engine. The combined total voltage drop should be no more than 0.3 to 0.4 volts.