how to check for draw on car battery

[SanMariana]

To check for a parasitic draw on your car battery, you need a digital multimeter (DMM) to measure the current flowing when the car is off and everything should be asleep. A normal parasitic draw is typically between 20mA and 50mA (0.020 to 0.050 amps). Anything significantly higher indicates an electrical issue that will drain your battery.

Step-by-Step Guide:

1. Safety and Preparation: Park the car in a well-ventilated area. Put on safety glasses. Turn off everything – ignition, lights, radio, and close all doors. Wait at least 30-60 minutes for the vehicle's modules to enter "sleep" mode. Unhook any aftermarket accessories like dash cams.
2. Disconnect the Negative Terminal: Pop the hood and locate the battery. Using a wrench, loosen the nut on the negative (-) terminal and carefully remove the cable. This breaks the circuit.
3. Set Up Your Multimeter: Turn your DMM to the DC current setting, usually marked with an "A" with a straight and dashed line. Start with the highest amperage setting (e.g., 10A) to avoid blowing a fuse in the meter. Move the red probe to the port for Amps (often labeled 10A).
4. Take the Measurement: Connect the multimeter in series. Touch the red probe to the disconnected negative battery cable and the black probe to the negative battery terminal. The display will show the current draw in Amps. If the reading is very low, you can switch the DMM to a more sensitive mA (milliamp) setting for a more precise reading, but be sure to move the red probe to the correct port.
5. Identify the Culprit: If the draw is excessive, you can find the source by pulling fuses one at a time from the interior and under-hood fuse boxes. Pull a fuse, watch the multimeter. If the amperage drops significantly, you've found the circuit with the problem.

Typical Parasitic Draw Standards	Acceptable Current Range
Modern Car (with numerous ECUs)	0.020 - 0.050 Amps (20 - 50 mA)
Older Car (basic electronics)	< 0.020 Amps (20 mA)
Problematic Draw	> 0.050 Amps (50 mA)
Common Causes	Trunk light, glove box light, faulty module, aftermarket stereo

[VanJuliana]

Grab a multimeter from any auto parts store. Disconnect the negative battery cable after making sure the car is completely off. Set the meter to measure amps and connect it between the cable and the battery terminal. If the number is much higher than 0.05, you've got a drain. The tedious part is pulling fuses one by one until the number drops, which points you to the faulty circuit. It’s a bit of a puzzle, but satisfying to solve.