How do i find what is draining the battery in my car?

Question

The battery is in good working order as is the alternater I have checked all interior lights but they are ok. The battery goes from a full charge to dead in about 3 days, any help would be great,thanks.

Answer 1

SadAct, I have some Sad Fact.
It really comes down to a process of elimination.
If you have a multi-meter it will help. If you don't you can still probably eliminate the circuit until you find whatever it is that is draining the battery.
Check all the obvious things first, is the trunk lamp staying on when the trunk lid is closed. I got in mine while my wife closed the lid on her Cadillac and sure enough the light stayed on. she had knocked the switch out of place loading grocery's.

Check The light under th hood as well. take them out and put them in the glove box if your in doubt. How about the interior lights, the doors control them they can be on during the day and you won't notice.

Under the hood, the alternator can have a bad diode and discharge the battery while still putting out a reduced output enough to keep the alternator light off. Disconnect the positive lead from the alternator ...did it spark a little as you removed it, if so there's your problem. Be careful don't touch that lead to ground, you'll have more problems.

If this isn't it we move to other possibilities.

I'll assume you don't have a meter:
disconnect the negative battery cable you will be be using this to test with.

When you get the neg. terminal off, tap the cable back to the neg. battery post. note the spark you get as you tap it on and off the post. go to your fuse panel and remove one fuse at a time, going back to the neg. battery terminal to check that spark, hopefully you will pull one of the fuses and the spark will be very small. that will be the circuit that is draining the battery.

if none of the fuses stop or largely reduce the spark, you will need to check for wiring problems, usually a wire short will clear itself by blowing a fuse or fusible link, so I don't think this is your problem.

Remember check the obvious things first.

HTH
Yours: Grumpy

Answer 2

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.
IF you have an external regulator try this

Answer 3

Simple Test for this problem.

With the key off and the underhood light removed.

Disconnect the Positive battery terminal cable then touch it back to the battery terminal.
If it sparks you have an electrical problem.

If it does not spark you have either an Alternator problem (no suffcient charge) or a battery problem, most likely sulfation from age if it is old.

If you get the spark, disconnect one fuse at a time until the sparking stops, that is your problem circuit.

Of course you can do this with a Multimeter if you so choose LOL

Answer 4

Way I was taught in the Forces was this (for emergencies in the field).
Connect a volt meter across the battery - it should read over12V if charged. Start the vehicle, Voltage reading should now be higher. Increase the revs to about 2,000rpm, voltage should increase and stay at new level (usually over 13V) until revs eased off.
If voltage does not increase, suspect charging circuit and this usually means a duff alternator.
Like I said, only a rough check, but it has helped me out over the years and you only need a meter.

Answer 5

Your battery is not in good working order if it goes dead in 3 days. Is it new and have you verified this with a battery testing kit? It looks like it is leaking charge. Best to get it replaced.

Answer 6

hi the battery must be old like 3 to 4 years.replace it

Answer 7

If your battery went dead, and you either recharged or replaced it, and you've checked the alternator, do you have something such as your car stereo hooked directly to your battery?

Answer 8

It is the Regulator. But when you replace the Regulator you should install a new Alternator at the same time.

Answer 9

Check the cars earth wires.

Answer 10

could be your starter motor.get your car put on a kts machine and they will diagnose where the fault is.the battery is not good workimg order.if it drains a few times it knacks em anyway.