I am new to this forum so please forgive me if I'm not following proper protocol. My radio went completely dead (totally blank screen) then if I let the car sit for 2 or 3 days the battery is completely dead. I have AAA and they keep saying it's a bad battery. They put the third new battery in two days ago and again it's dead. No charge for the batteries but I need to find the cause and Don't know where to start. I was hoping someone could point me in the right direction. It's an '04 coupe and totally stock. Any help will be greatly appreciated. Thanx

 

It can be only one of two things:

1) Something in the car is draining the battery. *Someone* has to disconnect a battery cable, insert a meter in line, and measure the current. Anything over .05 amps (50 milliamp) is out of specification.

2) The Alternator is not charging the battery. Easiest way to find this is to measure battery voltage right at the battery with the engine off. You should see 12.4 or so volts, but anything from 11.8 to maybe 12.9 is fine. Now, start the engine and have someone rev it to 2000 rpm or so. Measure battery voltage - if the alternator is charging, you will see 13.5 to 14.4 volts.

Guessing at various items is a total waste of time. Use a meter and KNOW what is going on. DO NOT pay some fool who is standing there guessing about what is wrong, telling you about how his uncle found battery drain by replacing fuses or whatever - if he can't use a voltmeter and ammeter, it's time for you to go somewhere else.

Of all the electrical problems you can have with a car, a battery that won't stay charged is the easiest thing you could encounter.

 

I agree wholeheartedly with proper troubleshooting procedures and instruments (a nice little DVM is often a freebie at HF) with the caveat that once you determine there is an excessive drain (200 ma will drain in a couple of days, 50 ma is spec after connected for a few minutes, >20ma is what I usually see in a quiescent state. ), then pulling fuses until it goes away is often the fastest way to find the causing circuit/component.

 

To be more specific ( in case you aren't an electrical genius like pizzaguy or padgett ) :
1. get your hands on a DVM ( Digital Volt Meter ) and set it to the milliamp setting. There is a separate socket for this different from the + & - sockets for reading volts.
2. Disconnect the negative battery cable ( the one toward the front of the car ).
3. connect the DVM in Ma scale between the cable and the negative battery post, check the reading.
4. open the under hood accessory fuse box ( on the driver's side ) and start pulling fuses one at a time while watching the meter.
If the meter goes from like 60 ma down to 20 ma when you pull a fuse, then find out what that fuse is for.

Get back to us when you find the offending fuse for more help.

Mark, Mr padgett : not trying to horn in, just seemed to me a bit more detail was needed here.

 

NP just on the HF DVM it is the 10A scale that is a different plug.


Also between 3 and 4 you may need to wait a few minutes for the reconnect/door open thingies like the interior lights to time out and turn off - may read more current until they do.

Now why did I need to put the post into manual mode to get the URL link to pop up ?.

 

If we are going to try to describe the actual procedure, then:

Don't do something like turn the headlights on, or turn the key to "on" with the meter connected as an ammeter -you will blow the fuse in the meter!

As Padgett pointed out, there will be, usually, two scales/ranges on the meter, one for about 10 amps and one for under .2 amp (200 millliamps). If you connect the meter on the lower scale and see NO reading - you have blown the damn fuse in the meter! So buy extra fuses for the meter when you buy it.

Also, there may be TWO fuses in the meter -one for the 10 amp scale and one for the .2 amp scale.


(Oh, and I'm an ELECTRONICS genius, not electrical. )
(Well, its more like savant syndrome than Genius. It's all really complicated - not Avril Lavine Complicated, just complicated.)

 

All good points. See ? I told you they were the geniuses ........

 

OK the "safe" way requires a jumper cable. Start on the 10A scale/connection. When you see it drop under 200 ma (0.20) then
1) connect the jumper cable across the leads
2) change the meter & input to the 200ma scale
3) remove the jumper


or just use the 10A scale for the whole procedure, can usually read to 10 ma and that is enough to see issues. Just make sure it goes to zero when disconnected.


Key and lights must be off. If interior lights are on wait for them to time out.


ps I do not claim genius at all. Others may...



Was a lot easier when cars were dumb.

 

Some people have called me an idiot savant, my brother will argue that it's proper to eliminate the savant. LOL