Parasitic Battery Drain

[Jaden01]

Hey SHO Gods, got another issue today. I realized my car's got a 1.5 volt parasitic drain from the battery when it's off. I've checked that no lights are on, no doors are open, and that it's not in the radio-only mode. When the car is sitting I am able to measure the voltage of the battery when it's connected, and when I disconnect the cables and I can see it's got that 1.5 volt drain. When the cars on, the battery shoots up to 14.44 volts which in my eyes means the alternator is doing it's job. What do you guys think is causing this issue?

 

[yaycandy]

Check on diodes. Not sure where they are but they can fail. They are the one way valves of electric. Almost every car has them somewhere. Sometimes they are in the dash, sometimes in the alternator itself or even in a power wire.

 

[Mike Spataro]

You may want to start by lowering the fuse panel under the dash and start pulling each fuse, one by one. Be sure to have the door switch in the off position. After removing a fuse, carefully touch the contacts with the fuse and notice if it sparks and it will reveal the circuit that is causing the drain. I found my dash light dimmer switch intermittently drains the battery in different positions. Good luck

 

[BaySHO Performance]

When the car is sitting I am able to measure the voltage of the battery when it's connected, and when I disconnect the cables and I can see it's got that 1.5 volt drain.

If you are saying there's a 1.5V drain with the battery disconnected, looks like it's on its way out. Have it load tested. Other common suspects are a car alarm or the hood light.

 

[SHOrod]

I'm not following what you're doing. Are you saying you measure the battery voltage when the battery is connected but the car is off, then you disconnect the battery and the battery voltage out of the circuit is 1.5 V higher than when the cables are connected? Are you performing this test because of an observed issue, or are you assuming there's an issue because you happened to observe the difference?

-Rod

 

[Greg Corcoran]

When the car is sitting I am able to measure the voltage of the battery when it's connected, and when I disconnect the cables and I can see it's got that 1.5 volt drain. When the cars on, the battery shoots up to 14.44 volts which in my eyes means the alternator is doing it's job.

Parasitic drain will cause the car to drain the battery to 'no start', slow turning or just clicking in anywhere from a day to a week. 1 take your battery to be load tested so you know it is good or bad. 2 if your car can sit a week and not drain the battery the 1.5V may be normal for your car (remember it needs some power to keep the ECU memory settings and radio presets, etc).
The last two (non SHO) cars I has with a true parasitic draw was bad voltage regulator on one, and bad diode inside the alternator on the other.
BTW you should use amp reading rater than voltage to tell if the draw is meaningful. With the meter between the battery cable and terminal note the amp reading change when the hood light is on and off. If you see a small fraction of that corresponding to the 1.5V drop then you are seeing the ECU and radio 'keep alive' draw and no need to worry.
Others may have different opinions.

 

[PaulTAutoX]

A battery will usually only drop voltage under a significant load, compared to its current delivery capacity. I'm surprised that you see a 1.5 V difference. What Greg C said, see what the amps are when there are no lights on to see what the drain is.

 

[luigisho]

I found my dash light dimmer switch intermittently drains the battery in different positions.

This issue used to pop up alot. It was more noticeable when we had a bigger GenI/II group back in the day where you could see patterns emerge with a much larger owner population.

 

[FastCAD]

Hey SHO Gods, got another issue today. I realized my car's got a 1.5 volt parasitic drain from the battery when it's off. I've checked that no lights are on, no doors are open, and that it's not in the radio-only mode. When the car is sitting I am able to measure the voltage of the battery when it's connected, and when I disconnect the cables and I can see it's got that 1.5 volt drain. When the cars on, the battery shoots up to 14.44 volts which in my eyes means the alternator is doing it's job. What do you guys think is causing this issue?

my 2cts.
do u have a lot of junk in your glove box? if so the glove box light can stay on without u knowing it with a 12v drain.
it happened to me.
pull the bulb and check your voltage again.