How to Check for Battery Drain in a Vehicle?
2 Answers
Methods to check for vehicle battery drain: First, turn off the car's ignition switch and wait for 5 to 10 minutes with the car locked, allowing it to enter a dormant state. Then, loosen the tightening nut on the battery's negative terminal and disconnect the negative cable. Set the multimeter to the DC 10A or 20A range, connect the red probe to the vehicle's ground wire, and the black probe to the battery's negative terminal. Finally, observe the multimeter reading directly. The normal value for vehicle battery drain is around 40mA, while some high-end cars may reach up to 80mA. However, if the battery drain is 90mA or more, it is definitely abnormal, likely due to abnormal drain in the anti-theft system circuit or other circuits.
I've been driving for over ten years and often encounter situations where the battery inexplicably dies, which feels like a parasitic drain issue. To check for this, the simplest method is to turn off the engine and close all doors, then wait for about half an hour to let the vehicle enter sleep mode. After that, use a multimeter to measure the current between the battery terminals. If the reading exceeds 50 milliamps, there's likely a parasitic drain. At this point, you should pull out the fuses one by one to see if the current drops, which can help identify the problematic component, such as a dashcam or GPS that isn't entering sleep mode. It's also good practice to regularly check if the headlights and interior lights turn off automatically, and to be cautious about wiring quality when installing non-OEM devices. Driving for at least half an hour regularly can help recharge the battery and prevent this issue.
