Parasitic Battery Drain

What is parasitic battery drain or phantom load?

A parasitic drain is an electrical load that draws current from the battery when the ignition switch is off.

How much load/drain is acceptable?

This depends on your battery size(CCA and AH) and condition. PCM/ECM, BCM, RKE, radio, alarm are some of the things that are designed to use a very small amount of current all of the time. Typical drain is about 7-12mA(0.007-0.012amp), with a max acceptable draw ~30mA(0.030amp).

If you are storing your van for more than 20 days, disconnect the battery and charge it every 20-45 days to maintain your battery. Another option is to use a battery maintenance charger(solar is my favorite).

Find your battery max drain amps, divide reserve capacity by 4 or amp hour rating by 2.4 = XmA. Example: RC of 100 minutes(60AH), current drain should not exceed 25 mA.

The chart below shows a 690 CCA battery with at 110 min. RC (60.5 AH) starting at 80 percent state of charge and how long until it will reach a 50% state of charge(aprox. as temp and ratings affect life).

Where to look first, it could be:

• • Human error - Leaving the glove box/door/hatch open, leaving lights on or a device plugged into the cigarette/power outlets/OBD2 port/etc.

  • Battery/charging problems - If your battery is old(5yrs?) it may not be holding a charge, or your alternator/diode is defective. Get your battery tested.

  • Super short trips - Doesn't give the alternator enough time to charge the battery.

  • Part failure - Stuck relays, door pin failure, glove box door warpage doesn't shut off light, failed ignition switch(rare).

  • Aftermarket alarms and stereos/amps - OEM alarms/radios/amps are usually not the cause, but if you have aftermarket accessories, look there first.

Tools used for testing:

Here are some of the tools that I use for testing.

• • • Battery disconnect - required to bypass the meter without breaking the connection. http://amzn.to/2pSpBiY can also use jumpers to the same effect.

    • Digital volt ohm meter - a decent meter is required for a lot of automotive testing, and it doesn't have to be expensive. See Tools

    • Plug in amp meter - extremely handy for quickly testing a circuit. http://amzn.to/2qPlwtb you can sometimes find these at HarborFreight, cheap. Can use a set of jumpers to test other sized fuses. Note: this is handy for larger loads, but a few of that type of tester can measure down low enough for phantom load testing.

    • 10amp fused jumper wire - easy to make using a fuse holder. http://amzn.to/2qPeAfE Fused jumper wires are a REQUIRED item for many testing procedures.

Testing for parasitic battery drain:

• 1. The goal is to insert the meter between the battery terminal and the rest of the automotive circuits so that all current flows through the meter. One of the easiest ways is to use the battery disconnect listed above with a fused jumper wire. Start out on the highest amperage setting on your meter, once the current flow drops below the lower setting on your meter, you can switch for a more accurate reading. Just make sure that you don't cause anything to power up/turn on while you are in the lower setting(think interior lights, RKE, etc) or else you can blow the replaceable fuse in your meter.

  2. You can also use your meter on opposite sides of each circuit fuse for a voltage drop reading, if there is current flowing through the circuit there will be a slight voltage drop across the fuse. This can quickly identify the circuit for more testing. See the Fuse Voltage Drop PDF . Also see Voltage Drop Testing

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Startup sequence:

When testing, you will find after you connect your battery/meter, the systems will go through a startup mode for about 2.5 minutes. Ensure that you monitor long enough to get an accurate picture of what is really going on. In addition, some modules can wake up periodically. Here are the testing results on my 03 without any excessive parasitic/phantom load:

• • 1.8a for about 8 seconds

  • 0.55a for another 20 seconds

  • 0.07a for about 2 minutes

  • finally settles down to 0.00a with an occasional 0.01a blip, could have tested this down even more, but once below ~20mA I consider it good to go.