How to Test for Battery Self-Discharge in a Car?
2 Answers
Methods for testing car battery self-discharge: 1. Turn off the car's ignition switch and wait for 5 to 10 minutes in the locked state to allow the car to enter a dormant mode; 2. Locate the tightening nut on the negative terminal of the battery, loosen it with a wrench, then use a flathead screwdriver to pry open the tightening block, and directly pull out the negative terminal connector; 3. Set the multimeter to the DC 10A or 20A range, connect the red probe of the multimeter to the vehicle's grounding wire, and the black probe to the negative terminal of the battery; 4. Observe the reading on the multimeter directly. If the reading falls within the normal range, it indicates that the car's leakage current is normal.
I've been driving for 20 years, and battery self-discharge is very common. The test is simple: park and turn off the engine, lock the doors, and wait patiently for 15 minutes to let the car fully sleep. Take out a multimeter, set it to the current measurement mode, and connect it to the negative battery cable to measure the current. The normal value should be around 30 to 50 milliamps; if it spikes above 100 milliamps, there's definitely something secretly draining power. My previous car had a 200-milliamp leakage, caused by an added GPS navigation module, which forced me to replace the battery. The solution is to pull out the fuses one by one—when the current drops after pulling one, you've found the source. Fix it promptly after testing; don't delay, or the battery will die, and your wallet will suffer. Just buy a decent multimeter; it costs only a few dozen bucks. For long-term parking, disconnect the battery cable as a preventive measure to ensure your car doesn't stall.
