Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hello, below is some information on battery draw that may help you. To track down the problem you will need to connect a DVOM between the negative cable end and the battery to take a reading. Just remember that some of the computers on the truck will take as long as 30 minutes to go to sleep, thus giving you a false reading until after they are asleep. Once you have disabled things like the dome lights and glove box and under hood lights, don't over look things like the alternator as even a bad negative diode in the alternator can cause a draw on the system when it is off. After the meter is connected, look for a draw of around 50 milliamp or so. The object being to unhook and disconnect circuits one at a time or remove fuses one at a time until you find the circuit that is causing the draw and makes the meter drop down below 50 milliamp. Then you know what circuit has the problem and is creating the draw on the system. If you have not already done so, you may want to have the battery load tested to make sure it is up to snuff. Big difference between being fully charged and being a good battery. See if the additional info below is any help. Thanks
This bulletin is being revised to add the 2004 and 2005 model years. Please discard Corporate Bulletin Number 02-06-03-010 (Section 06 - Engine).
In automotive terms, a parasitic drain is an electrical load that draws current from the battery when the ignition is turned off. Some devices, such as the PCM and the radio memory are intended to draw a very small amount continuously. These draws are measured in milliamps (mA).
In normal use, parasitic drains aren't usually cause for concern, because the battery is replenished each time the vehicle is driven. But, in long-term parking situations, parasitic drains may discharge the battery enough to cause a no-start condition. New vehicles in dealer stock and airport long-term parking are two such situations.
An abnormal parasitic drain could be a glovebox or luggage compartment light that remains on but undetected. Or an electronic component may malfunction and cause a parasitic drain that is larger than normal specification.
Parasitic Drains and On-the-Lot Battery Discharge
Important: In most cases of discharged batteries in low-age, low-mileage vehicles, proper charging procedures with approved charging equipment is the only repair necessary.
Here are some rules of thumb that might help relate parasitic drains to how long a battery would last on a parked vehicle.
The Reserve Capacity (RC) rating multiplied by 0.6 gives the approximate available ampere-hours (AH) from full charge to complete rundown. Somewhere between full charge and complete rundown, the battery will reach a point at which it can no longer start the engine, although it may still operate some of the electrical accessories.
Using up about 40% of the total available AH will usually take a fully-charged battery to a no-start condition at moderate temperatures of 25°C (77°F). Put another way, for a typical battery in a storage situation, depleting the available AH by 20 to 30 AH will result in a no-start condition.
Important: If the battery begins storage at 90% of full charge, reduce the available AH accordingly.
The recommendation for maximum parasitic drain is around 30 mA (0.030 amp). A typical drain today actually falls into the 7-12 mA range, even though some vehicles do approach the maximum. Multiply the drain (in amps) by the time (in hours) the battery sits without being recharged. The result is the amount of AH consumed by the parasitic drain. The actual drain may be small, but over time the battery grows steadily weaker.
Here's an example: a vehicle with a 30 mA drain and a fully-charged 70 RC battery will last 23 days. But if that battery is at only 65% of full charge (green dot barely visible), it is going to last only 15 days before causing a no-start.