How to Find a Parasitic Battery Drain


Si la batería de tu automóvil amanece muerta generalmente es porque ya llegó al final de su vida útil o dejaste algún dispositivo encendido, como por ejemplo una luz. Ocasionalmente algo que está fuera de tu control ocasiona que la batería se drene. Esto se conoce como una fuga parásito y puede ocasionar el mismo resultado que dejar los faros delanteros encendidos, una batería muerta.

1. Remove the negative side battery cable from the negative battery terminal.

2. Connect the black wire to the com input on a multimeter and the red wire to the 10A or 20A input on the multimeter. The meter needs to be able to read at least 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won’t work and could damage the meter.

3. Attach a multimeter (set the dial on the multimeter to measure Amps as per multimeter instructions) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode — i.e. when you make the contact with the ammeter, the car’s computer systems “wake up.” After a bit of time they will go back to “sleep.”

4. If the ammeter is reading over 25–50 milliamps, something is using too much battery power.

5. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings) last. Perform the same steps on all relays found in the fuse panel. Sometimes relay contacts can fail to release, causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.

6. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners’ manual or service manual to find what circuits are on that fuse.

7. Check each device (circuit) on that fuse. Disconnect each lamp, heater, electrical device one at a time to find the drain.

8. Repeat steps 1 & 2 to test your repair. The ammeter will tell you exact numbers.

9. Try unhooking the big wire from your alternator. The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator’s power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal. This will drain a battery pretty quickly. Make sure to read the ammeter before and after unplugging your Alternator.

Things you´ll need:

  • Digital multimeter or ammeter.
  • A fuse puller. (You can also use pliers, but try not to crush the fuse.)
  • Any tools needed to access battery and fuse panel(s).
  • An owners’ manual or maintenance manual showing electrical circuits.