I have an 88 IROC in which the battery keeps losing voltage when the car is completely off and no electronics, lights, etc. are on. I can charge the battery, and it appears my alternator is working as my capacitor is indicating a charging voltage. Then when I shut the car off, I will have at least 12 volts in the battery. However, after sitting the battery will slowly be drained down. Right now, the battery is showing 2.70 volts with the pos and neg wires connected. When I disconnect both of them, I get around 5.70 volts. However, when I just disconnect the negative cable and measure the amperage draw between the negative wire and the negative terminal of the battery, I am getting readings below 20 mA (they are fluctuating readings, but there is an alarm system and motion sensor in the car and I am not sure if that is part of the fluctuation). Any suggestions?

 

Also, the battery is only a couple months old, as the previous one wouldn't hold a charge and the auto parts store tested it and said it was bad.

 

It's a longshot - but with key off, put ear against gas tank and listen for the fuel pump.

The OPSU can go bad in such a way that it senses oil pressure when there is none, and thus makes the fuel pump run constantly. This takes about 24 hours or so to drain a fully charged battery - if your is draining faster, might be something else.

 

i have an aftermarket fuel pump in there that is quite audible when running and I do not hear it at anytime

 

I read elsewhere that an amperage draw of less than 50 mA would not kill a battery like this. Is this true? Is it possible the battery could be bad already?

 

take a volt meter and put it inline on the power cable - So disconnect the battery and check the draw (voltage) between the cable and the battery. If you have a high reading start pulling fuses until the reading goes away. That should point you in the right direction as to what is draining your battery. Be aware the reading will go up when you open the door (interior lights), so you should rig the switch to show to door closed.

 

How high do you mean by a high amperage reading? With everything plugged in and no fuses out, the amperage draw was less than 20 mA. I just did an experiment using voltage. Battery isn't fully charged, but without any cables attached to it, the voltage is like 5.70 V. With both cables attached the voltage is 2.70 V. I pulled every fuse and the checked the voltage each time and it remained at 2.70 V every time. I unplugged my alarm system module, and it went up to 3.5 V, but still not up to the 5.70 V it is with everything unplugged from it.

 

I would get the battery charged to it's normal level and then start testing. The limit is 50ma so 20ma shouldn't be killing your battery, but you should be testing this over a few hours. There is a chance that whatever is killing your battery could be turning off and on.

 

So here is the latest, and please forgive me for sounding like an idiot with some of these measurements, but I charged the battery to 12.10 V. I unplugged the positive battery cable from the terminal and hooked a multimeter between them. The current reading on the 10 Amp scale is .05 (which I am assuming would be 50 mA right?) If I unplug the wiring for my audio system (capacitor + amp), the reading drops to .03 (30 mA). Would this be considered an acceptable amperage draw? What would be causing the audio system to draw this amperage if nothing is on? Also when I got those voltage readings mentioned in the above posts, having the audio system cable unhooked from the positive cable did not explain the voltage drop seen between having the positive cable hooked up to the terminal and not having it hooked up

 

OK, I don't have any experience with audio capacitors, but shouldn't it continue to draw from the battery until it reaches it's desired voltage level? If this is true, then the capacitor would be what is killing your battery. Try taking it out of the equation and retesting to see if the battery dies.

In my experience (12 yrs) your battery draw typically doesn't exceed 20ma.

 

OK, I took the audio system (capacitor and amp) out of the line and hooked the positive cable back up. Reading on the battery right now is 11.90 V

 

7:00 P.M.: the battery voltage with all leads connected except for audio system is 11.84 Volts (3 hours ago it was as 11.90 volts).

 

The battery did not die overnight (it is at 11.81 Volts now), which means my audio system is draining the battery when the car is off. This system consists of a capacitor, amp, two subs and two 6 x 9s. Anyone have any ideas what could be wrong here or how to proceed? Thank you

 

On computer conrolled vehicles, the ECM's memory is kept alive by the use of a small electrical current. This alone will account for 20miliamps. The clock memory will draw another 20mA We do not consider parasitic power loss a problem unless it exceeds .2 amps which is 200mA. The capacitor will draw power until it is at equal charge to the battery. It will not drain the battery.

Try switching to the mA scale to verify draw of 50mA. If this is in fact your systems key off power draw, and your battery is going dead after a few days, test or replace the battery. BTW, full charge on a 12v automotive battery is 12.6 volts(2.1 x 6).

 

I took the battery to advance auto parts and they tested it. It came back at 11.58 V and 34 cranking amps (the battery is rated for 650). I drove the car yesterday late yesterday for a little bit and charged the battery back up. Also, the audio system was unplugged over night. I just hooked the negative cable back up to the negative terminal on the battery, and then i hooked the positive probe of my multimeter to the positive terminal on the battery and the negative terminal to my positive battery cable (with my audio system line connected). The initial draw on the 10A scale on my multimeter was 0.13 (which i am assuming is 130 mA?) while the capacitor was lit up and i am assuming equilibrating with the battery. Then, when the lights and voltage display went off, the multimeter has been reading 0.06 on the 10A scale (I am assuming 60 mA). All other electronics are off, doors are closed, no lights on. Does this sound right?

 

Yes. Infact that's very low draw for a computer controlled vehicle. No more battery drain? Sounds like your battery had a bad cell.

Just for information sake, the OE battery in any modern electronically controlled vehicle will hold a charge in storage for about two months. Bigger batteries with higher AH ratings will last longer. The best are the deep cycle like the Optima yellow top. Any longer than that and it's a crap shoot. Ambient temperature plays a big part. In colder temps, batteries lose their charge faster.

 

I had advance auto parts charge the battery over night. Their reading this morning was 13.30 V with 713 cranking amps. It appears the battery is good. I just hooked it back up the car and have my multimeter in line between the positive cable and positive battery terminal with all electronics hooked up and everything off. The current draw is 55 mA. I am gonna watch this and see if the battery dies.

 

Battery is not dead yet, but the voltage is down a little to like 13.1, 13.5 volts. It was drawing 60 mA all day with nothing running. Tested the voltage then hooked the multimeter back in line and its reading 80 mA. Not sure what changed the draw. I didnt do anything else.

 

13 volts is high for the battery at rest. A fully charged 12v wet cell battery should read 12.6v. 80mA is still well below the upper limit.