Both of my batteries died overnight in my truck what could of caused this?

Question

I have a 2003 GMC Sierra with a Duramax Diesel. It's all electronic and this morning I couldn't start my truck, both batteries had died completely overnight. It couldn't even be jumped. What could of caused this?

the trucks lights are automatic and turn off on their own. no lights were left on.

I know about glow plugs and that's definately not it, seeing as it's 100 degrees outside.

Answer 1

You need a AVR test. (AVR - Amperage/Voltage/Resistance) This test checks out the charging and starting systems on your vehicle. The mechanic will check all the battery connections, cables, alternator, starter, and battery. They normally charge a hour for this diagnosis, and wave the charge depending on what they find for the repair.

I assume you didn't leave any lights on...

As a educated guess... I would say faulty battery connections or even faulty batteries. Your truck is too new for corroded cables, faulty starter (unlikely due to your complaint), faulty alternator (unlikely due to your complaint).

Answer 2

You may have a bad alternator. Also, one battery can fail and draw the other one down. You could also have an electric drain.

You first should charge the batteries. If the truck then starts normally, the batteries are probably OK. Put a voltmeter across the terminals of either battery while the truck is running. You should get a reading of 14.2 volts or so. Lower than 13.8 and you FOR SURE have a charging problem.

if the voltage is OK then you have a drain somewhere. Disconnect the battery cable closest to the car's electric system (hard to describe in a 2 battery system: maybe the easiest way is to completely disconnect one battery, leave the negative attached on one battery and leave the positive disconnected on the same batttery) Put a test light between the disconnected terminal and the battery cable. If the light lights up, you have a drain capable of draining the battteries. Disconnect fuses one at a time until the light goes out: then you will have found the drain.

Make sure to try disconnecting the alternator as a part of this test: they can drain thorough a diode and still provide a charge!

The alternator generally doesn't have a fuse.

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Answer 3

This is a good question first are the batteries both dead the gm cars use a side terminal battery post you need to check for corrosion at the post at first glance they may look ok but the problem lies below remove the cables from both batteries some will have one cable and some 2 depending where they are now clean post where bolt goes and then take a small screwdriver and pry the insulation off the cables and look for a white power if found dip cable end and a small cup of water and about a tablespoon of arm and hammer baken soda it will foam up this will clean it reinstall covers and install cables and try again if that doesn`t repair it remove batteries and take to a parts store and have them checked most check them for free if they are good check alt.

Answer 4

No one is going to be able to tell you exactly what is wrong, A vehicle's electrical system is very complex. It could be a mulititude of things going on. It is for sure and for certain that if you truck was ok the day before and wouldnt start the very next morning it is obivious that something is draining your batteries. Now before I go too far, are you sure that the batteries are dead? test them separately, if they are dead, then what I said earlier is evident, something is draining them. Have it checked out by a reputable mechanic that has expert knowledge in a vehicle's electrical system or take it back to your dealer if it is still under warranty. It could be something simple, or it could be something more complex.

Answer 5

Do you know for sure that both batteries are dead, or are you assuming this because the jump failed? Test each battery separately. You may find one is good and one is shorted, draining down the good battery. It's not likely both would go bad at the same time, although that is possible. It could be, as suggested, alternator, or a drain somewhere drawing them down.

Call GM and have them come tow it in and fix it, whatever it is.

Answer 6

Sounds like perhaps a grounding problem somewhere in the electrical system. Or something isn't turning off with the key. An example could be...the ecu, radio, radio light, interior lights. You mentioned the lights are automatic. Maybe something could be wrong with that, or maybe their is a faulty unit just drawing juice for no reason

Answer 7

Maybe you left the lights on inside or outside.

Answer 8

Maybe leaving some lights on overnight; maybe a failure of the alternator; maybe you used them for three years and that is their normal life span.

Answer 9

alternator

Answer 10

If your altenator is good, then it is possible that your break light switch may be weak allowing it to stay on and causing your break lights to stay on. just a thought.