IK0800025 ­ Measuring Parasitic Battery Load

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Title : Measuring Parasitic Battery Load
Applies To : All Vehicles

CHANGE LOG
Please refer to the change log text box below for recent changes to this article:
06/30/2015 - Author updated for feedback purposes
04/03/2017 - Updated 500K draw spec

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Description
Measuring the current draw on truck batteries when everything is turned off is required to evaluate the parasitic
battery load when the vehicle is not in use. This procedure will describe the steps required in order to measure
this at rest current draw or parasitic load of the vehicles electrical system.

NOTE:
If the vehicle has an AWARE module on it, make sure that it is updated. It should have a Kernel number
higher than 86. If the Kernel is lower than 86, the AWARE module could be causing a battery drain.
NOTE:
You may notice the blower motor turn on for a brief moment when the batteries are re-connected. This is
normal. For more detailed information please refer to IK1900212 - Front Blower Motor Runs Breifly At
Initial Power Up

Procedure
1. Switch off all electrical loads such as lights, radio equipment, auxiliary equipment and make sure the vehicle
ignition system is turned off.

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2. Identify the ground paths from the negative battery terminals to the frame, engine starter, or other electronic
devices such as the TCM, ECM, and Body Controller (ESC).
3. Remove all ground paths from the negative battery terminals. In the example shown in Figure 1, the main
battery ground feed goes from the forward battery negative stud (A) to the starter motor, the frame ground
(B) from the rail to the rear battery negative stud, and the clean power and ground feed (negative side)
which attaches to the negative jumper cable (C) leading from the forward battery negative stud to the rear
battery negative stud. This jumper must be disconnected from both batteries.
Figure 1

4. Connect the two ground cables (main starter feed (A), frame ground feed (B), and the jumper with clean
power ground (C)) together. This can be done by simply bolting the three cable eyelets together as shown in
Figure 2
5. Make sure they will stay together and that you can place a jumper lead onto the connected eyelets or bolt
and the negative battery stud as shown in Figure 2
Figure 2

6. Connect a jumper lead from the three connected ground cables to the negative battery terminal as shown in
Figure 2. You are now feeding the electrical current requirements of the entire vehicle through the jumper
lead. Do not activate any other electrical equipment while the jumper lead is supplying the vehicle current.
Wait five minutes to allow all electrical devices to shut down and go to standby mode.
7. While waiting for the vehicle electronics to go to sleep, set up a digital ammeter, such as the Fluke 88 shown
in Figures 2 & 3 to read amps (automatic scale) and make sure the test leads are plugged in to the correct
connectors to read amps (COM and A).
8. Connect the COM ammeter lead to the negative battery stud and the positive lead to the three connected
ground cables. Your batteries should now be configured like Figure 2.

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IK0800025 ­ Measuring Parasitic Battery Load

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Figure 3

9. After five minutes with the jumper and the ammeter connected in parallel, remove the jumper lead from the
three connected cables to the negative battery stud as shown in Figure 3. The vehicles entire current
requirements (parasitic load) will now be going through the ammeter. Read the current flow in milliamps.
Remember that 1000 milliamps is equal to 1 amp. If the readout has ma after the reading youre measuring
milliamps, if the readout has A after the reading youre measuring amps. If at any time during this process the
current flow is interrupted (a connector falls off) you must begin again with the jumper connected for five
minutes before attempting to remove it leaving the ammeter passing all current and measuring the parasitic
load.
CAUTION: If the digital ammeter by itself is used to complete the circuit (without the jumper) it is very likely that
the instantaneous current surge will blow the fuse in the ammeter. Always connect the jumper first and after
five minutes connect the ammeter in parallel, lastly disconnect the jumper to read milliamps flowing
through the ammeter.
10. Under normal conditions, while parked, a vehicle equipped with a standard electronics package should be
drawing less than 50 milliamps (500ma draw in 500k vehicle is typical). If the parasitic load is
more than this the vehicles battery storage life will be shortened.
11. If excessive current draw is observed, remove the fuses one at a time until a significant current drop is
noted. Do not pull and reinstall the fuses as this may wake up some circuits and cause excessive surge
current through the meter. Make note of fuse locations as they are pulled so they can be reinstalled in the
proper fuse panel location when testing is complete. When high current draw devices are isolated consider
relocating their power feed from a power source that is inactive when the ignition switch is turned to OFF.

NOTE: In order to ensure all modules stay asleep and you get a clean accurate
reading, you will have to keep the doors closed, with any door open, or
opening a door while taking your readings will cause several modules to wake
up and your reading will jump up. Recommend leaving windows rolled down so
you can still have access to fuse panel if an excessive draw is noted.
Additional Battery Connection Example
In this example, there are four batteries with three ground cables that have to be disconnected from the negative
battery posts. See Figure 4.
Disconnect the main ground cable that runs from the upper left batterys negative (A) terminal, the frame ground
cable (B) that runs from the frame rail to the upper right batterys negative (-) terminal, and the cable (C) that
connects the two lower battery negative terminals and the ground side of the clean power and ground cable.
Once disconnected these three cable ends should be bolted together and jumpered from this bolted joint to one
of the negative battery terminals as shown in Figure 5. After jumper is connected the ammeter should also be

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connected so it parallels the jumper like discussed in the previous example. Lastly the jumper is removed and the
ammeter is read for parasitic current draw as shown in Figure 6. As with the previous example, always wait five
minutes after the jumper is connected before installing the ammeter leads and removing the jumper.
Figure 4

Figure 5

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Figure 6

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