Parasitic Battery Causes and Remedies



      Parasitic loads are caused by electric devices which consume power even when they are turned off.


An example would be your household TV—while the TV may be turned off, the electronics are consuming a small amount of power so the “instant- on feature” can turn on the TV without a warm-up period.


An example on late- model automobiles would be after shutting off the engine, the ECMs/engine control module remains wide awake for a predetermined time all’s ready for an immediate engine restart. This higher-rate parasitic draw from the chassis battery can approach 30 minutes before the system goes to sleep and the parasitic draw is reduced.


Simply, one must have a working knowledge and understanding of the electrical equipment on a specific chassis/specific vehicle to be able to determine what draw is “normal” and what is not.


      Unfortunately for the end user, the typical operator manual doesn’t share detailed information like this so getting acquainted with a new vehicle can be an adventure!


      Here are a few examples of some common equipment found in a typical RV that can place a parasitic load on the 12-volt electrical system:


On the Chassis battery side:


• Electric slide out rooms (control module)

• Electric steps (control module)

• Automotive radios (memory)

  • Chassis OEMs equipment (engine/ transmission ECMs)

On the Coach/House battery side:


• 12V TVs

• Inverter/Chargers

• LP tank shut-off valve (electronic solenoid valve)

• Illuminated touch pads (Firefly – Multiplexed Electronics Package)


 For the curious folks, here’s a link to a video that provides some insights regarding how to test for a parasitic draw on

an automotive battery: https://www.


Countermeasures: There are significant differences in the electrical equipment commonly found in a Class B versus a Class A model…not to mention the size and capacity of their respective battery packages, so owners must be proactive in getting acquainted with the equipment on their specific model coach.


Even an experienced veteran that has owned multiple RVs must take the initiative to educate themselves with a new model or risk another round of “hard knocks.”


Parasitic loads are a reality and the easiest method to avoid a low-battery condition or permanent damage to the battery package while the vehicle is sitting idle (or in storage), is to use the battery disconnects provided.


So Folks... Watch those Parasites!

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