battery dies after 4 days
Thread Starter
3rd Gear
Joined: Aug 2005
Posts: 3
Likes: 0
battery dies after 4 days
I need some help. I have a dead battery after about 4 days of not driving the vehicle. I have had the alternator checked out and it is charging, I put in a new battery and even installed a Priority Start to isolate the battery if the voltage drops too low. The Priority Start does disconnect the circuit but when I step on the brake pedal to reingage the circuit, the battery is too dead to start the vehicle. Any help would be greatly appreciated.
Thread Starter
3rd Gear
Joined: Aug 2005
Posts: 3
Likes: 0
I tried that. Even went so far to see if there is a voltage drop from the battery as i pulled each fuse. No luck. It just doesn't make sense. The priority start is supposed to disconnect the circuit if it drops below 11.9 volts.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
You need to look for current drain, not a drop in voltage. A fully charged battery should hold a 12v level even with a slight drain on it.
Use a voltmeter and select the amperage setting to find the loss by pulling fuses. You need to connect it between the batt cable and the terminal.
Use a voltmeter and select the amperage setting to find the loss by pulling fuses. You need to connect it between the batt cable and the terminal.
Le Mans Master
Joined: Oct 2004
Posts: 5,841
Likes: 19
From: CLT, North Carolina
Diagnosing Current Draw
Key left in the ignition is a 1/4 amp constant draw because the VATS chip energizes the ECM when it is engaged. Are there any added aftermarket accessories such as radio or alarm? Disconnect the negative battery post and put an analog voltmeter in series with the disconnected terminal and the battery post and pull fuses one at a time till you find the one that causes the voltmeter reading to drop. Look in the service manual to see what equipment is on that fuse.
Regards, Greg
Regards, Greg
Melting Slicks
Joined: Sep 2003
Posts: 3,474
Likes: 1
From: 1
Originally Posted by Greg Gore
Key left in the ignition is a 1/4 amp constant draw because the VATS chip energizes the ECM when it is engaged.Regards, Greg
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Originally Posted by Greg Gore
Key left in the ignition is a 1/4 amp constant draw because the VATS chip energizes the ECM when it is engaged.
Additionally, I have an '88 that does exactly the same thing (battery draining). When I get the time, I plan to instal an amp meter to determine which cicuit is draining the battery.
Thanks for this important advice.
Aaron
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Its an AMMETER that you put in series between the battery post and the removed battery cable (the negative one because its the safest to remove) to measure leakage current. Start the ammeter out on a high range because when you connect the ammeter up the courtesy lights will come on. When they time out, switch to lower full scale current to measure the leakage current, it should not exceed 50 milliamps, my 87 draws 27 ma.
At night check for underhood lights, vanity mirror lights, console compartment light. Do you have a radar detector, aftermarket alarm or radio or audio amplifier? check em. Then pull the fuses one at a time (first pull the courtesy light fuse so you can keep the door open with the courtesy lights off) and watch the ammeter for a drop in current. If no drop, then remove the nut on the jump start teminal behind the battery (on early C4's, you don't say what year you own) and remove the 8 wires one at a time and also look for a drop in current.
Now.....your Priority Start is useless because a car battery at 11.9 volts is considered discharged ! Actually lead acid batteries are considered discharged at 12.0 volts and below and fully charged at 12.9 volts and above. Good luck.
At night check for underhood lights, vanity mirror lights, console compartment light. Do you have a radar detector, aftermarket alarm or radio or audio amplifier? check em. Then pull the fuses one at a time (first pull the courtesy light fuse so you can keep the door open with the courtesy lights off) and watch the ammeter for a drop in current. If no drop, then remove the nut on the jump start teminal behind the battery (on early C4's, you don't say what year you own) and remove the 8 wires one at a time and also look for a drop in current.
Now.....your Priority Start is useless because a car battery at 11.9 volts is considered discharged ! Actually lead acid batteries are considered discharged at 12.0 volts and below and fully charged at 12.9 volts and above. Good luck.
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Le Mans Master
Joined: Oct 2004
Posts: 5,841
Likes: 19
From: CLT, North Carolina
Stand by my Advice
Voltmeter will work too, try it. Reason I suggested it is because more folks have a $10 Radio Shack Micronta volt-ohmeter than have a good ammeter. When you find the draw and remove it from the circuit the series voltmeter reading will drop. Here's another one (food for thought): did you know that if you place voltmeter leads across the starter cable and cranked the engine the voltmeter would probably read about about a volt and a half (potential difference between one end of the starter cable and the other)?
Regards, Greg
Regards, Greg
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
A voltmeter will not work! I think what you are trying to say is that most people have a Micronta VOM (voltmeter, ohmeter, milliameter). Now that will work if the VOM is switched to measure current, although the cheaper Micronta VOM's may not measure high enough current to not be pinned by the courtesy light current.
I should have been more specific about what kind of ammeter to use, I meant that a decent VOM can be used to measure the leakage current. Most modern digital VOM's can measure 10 to 20 amps on their highest scale and can be switched down to the 100 ma. range to read the leakage current after the courtesy lights time out.
I should have been more specific about what kind of ammeter to use, I meant that a decent VOM can be used to measure the leakage current. Most modern digital VOM's can measure 10 to 20 amps on their highest scale and can be switched down to the 100 ma. range to read the leakage current after the courtesy lights time out.
Le Mans Master
Joined: Oct 2004
Posts: 5,841
Likes: 19
From: CLT, North Carolina
The Reason Why a Voltmeter Will Work
A voltmeter will work because an accessory that is drawing current presents a resistive load to the voltmeter causing it to read battery volts. On a known good electrical system disconnect the negative battery cable and connect a voltmeter in series with the battery post and the disconnected cable. If everything is OK the meter will read "0". Now open a door and watch the interior lights cause the meter to jump up to 12.8 volts. Agreed?
Drifting
Joined: Dec 2000
Posts: 1,833
Likes: 4
From: Calgary, Alberta
Originally Posted by jfb
Its an AMMETER that you put in series between the battery post and the removed battery cable (the negative one because its the safest to remove) to measure leakage current. Start the ammeter out on a high range because when you connect the ammeter up the courtesy lights will come on. When they time out, switch to lower full scale current to measure the leakage current, it should not exceed 50 milliamps, my 87 draws 27 ma.
At night check for underhood lights, vanity mirror lights, console compartment light. Do you have a radar detector, aftermarket alarm or radio or audio amplifier? check em. Then pull the fuses one at a time (first pull the courtesy light fuse so you can keep the door open with the courtesy lights off) and watch the ammeter for a drop in current. If no drop, then remove the nut on the jump start teminal behind the battery (on early C4's, you don't say what year you own) and remove the 8 wires one at a time and also look for a drop in current.
Now.....your Priority Start is useless because a car battery at 11.9 volts is considered discharged ! Actually lead acid batteries are considered discharged at 12.0 volts and below and fully charged at 12.9 volts and above. Good luck.
At night check for underhood lights, vanity mirror lights, console compartment light. Do you have a radar detector, aftermarket alarm or radio or audio amplifier? check em. Then pull the fuses one at a time (first pull the courtesy light fuse so you can keep the door open with the courtesy lights off) and watch the ammeter for a drop in current. If no drop, then remove the nut on the jump start teminal behind the battery (on early C4's, you don't say what year you own) and remove the 8 wires one at a time and also look for a drop in current.
Now.....your Priority Start is useless because a car battery at 11.9 volts is considered discharged ! Actually lead acid batteries are considered discharged at 12.0 volts and below and fully charged at 12.9 volts and above. Good luck.
On my '88 it was a combination of the vanity mirrors and 1 hood light staying on. It took about 5 to 6 days to drain my battery. Park on Sunday no Start Saturday......
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Originally Posted by Greg Gore
A voltmeter will work because an accessory that is drawing current presents a resistive load to the voltmeter causing it to read battery volts. On a known good electrical system disconnect the negative battery cable and connect a voltmeter in series with the battery post and the disconnected cable. If everything is OK the meter will read "0". Now open a door and watch the interior lights cause the meter to jump up to 12.8 volts. Agreed?
Decent voltmeters have an internal resistance that is very high, over a million ohms and when put in series with the battery will read the battery voltage all the time because the normal leakage resistance is way lower than a million ohms and very little voltage drop will occur across the leakage resistance and all of the voltage drop will occur across the voltmeter causing it to read the battery voltage. And anyway, what you are trying to determine is HOW MUCH the leakage current is to determine if it is normal or not (GM says not more than 50 milliamps).
