What is the normal voltage generated with your car running?? I noticed my voltage fluctuates from 15V to 12.5V. Is this normal? It gets up to 15V sometimes when i just start the car up on a hot day. Then it gradually gets to and stays around 14.3 or 14.4. At night when i have the headlights on, its around 14.1. When using headlights, AC, turn signals, and stopped a light, voltage sometimes drops to 12.5. Is this normal? I've also been noticing that if i don't drive my car for a day, the voltage of the battery is only around 11.2V when i turn the key to the On position. It should be around 12V or more right? What can i do to check for battery leakage or usage while the car is off? Thanks in advance..

 

Everything sounds normal except for battery voltage after car sits for a day. Voltage should be about 12.5 volts not 11.2, sounds like battery doesn't hold charge properly anymore. Your lucky it starts.

 

more likely the alternator is on its way out. voltage shouldn't run that high upon intial startup. if the alternator has bad diodes or voltage regulator in it, it can also cause drain on the battery while the car is off.

try disconnecting the cables on the alternator overnight and see what your battery voltage is in a day or so. if the voltage is still above 12V, then there's something funky with your alternator and it's time to rebuild/replace.

also, you can use a multimeter with an ammeter function on it to test for current drain. read the instructions on it to find out how, but for drain currents as low as what you're talking about, you can probably just disconnect the battery cable and stick the ammeter in line with the battery... DO NOT try to power any accessories when doing that, or you'll blow the maultimeter up though. just use it to test for leakage currents.

start narrowing it down by disconnecting one wire at a time from the + terminal on the battery, then you'll be able to trace it back to the source and see where it's being drawn from.

 

I'm with karguy on this.

Everything is normal except for the initial 15V, its high b/c the alt is trying to rapidly charge the batt. I'm guessing the batt is old, so go ahead and replace it.

The alt sound like its fine.

 

Thanks for the responses.

The battery in my car is a new Die Hard Gold. i just put it in a month ago after the previous one died. The alternator is about half a year old and is about the third one i've gone through. So when it puts out 15V, does it mean that the battery is drained and quick replenishment? I noticed it only happens when its hot out.

Matt - when you said to disconnect the alternator from the battery overnight and then check the voltage the next day, did you mean that if there is less than 12V then the alternator bad?

So is it normal for the voltage to drop to 12.5 while using the AC, head lights, turn signals, and stopped at a light?

Thanks for your help.

 

Check the tension on the Alt belt. It might be sliping a little on you.

 

Sounds normal to me.

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