The vehicle's battery is for starts(connected directly to and powers the starter motor and solenoid), running accessories with the ignition in "ACC" position, storing alternator(driven by engine and belt unit that creates voltage) voltage output and acting as a buffer for alternator voltage (to prevent damage to electronics). When the car is running the majority of the electrical current and voltage comes from the alternator.

ATTENTION: If you have a very low battery reading, under 5 volts or so, DO NOT attempt to jump start or charge the battery as it could have whats called a "shorted cell", the battery could explode, let a professional handle the car's charging system issue or replace the battery. ALSO it may seem obvious but batteries contain a very high level of potential energy (several hundred amps) and placing anything conductive, yes, like a wrench, between the two terminals can be extremely dangerous, be careful.

If your car is running and the battery light is on, its pretty much a 90% chance your battery died. The battery light however is technically a charging system light and illuminates when the variable voltage of the electrical system drops below a certain point so the issue could be the alternator itself, the battery, wiring, connections or other electrical system components. The alternator is designed to maintain 12.2 volts (Volts-The p.s.i. of electricity, (force or pressure)) throughout the electrical system and at the battery terminals, however it is also designed to put out more than 12.2 volts when the engine is running, 14.4 in total system voltage to be exact. An electronic device called a multimeter is a device used to take readings of electrical circuits and components, they can be fairly expensive but are a good tool to have. The cheaper ones will do for most of what were talking about as we're just taking voltage readings. Placing a multimeter on the battery ground and the battery positive terminals should yield roughly 12.2 volts with the engine off, if so you've got a battery that should not cause the battery light to illuminate, (due to the complexity of a battery's makeup a 12.2 volt reading does not 100% mean the battery is fully operational so we will continue to diagnose). Thus far you have 12.2 volts at the battery, your car starts and you have a battery light. You are looking at a 99.9% chance of a bad alternator situation, especially if symptoms include dimming headlights, gauges etc. To test more: With engine running @2000rpm a multimeter should show 14.4 volts at the battery's positive and negitive terminals, this should verify that you have an operational charging system and alternator , if not your problem is either an alternator, in wiring or in connections(voltage drop,excessive resistance) OR, a bad battery. To test, try moving the multimeter's positive test lead to the positive output terminal on the alternator, you should have 14.4 there, if you do then your problem is in wiring, connections or your battery and not the alternator.

I'm pretty sure Autozone and AdvanceAutoParts will test your alternator for you but they use a countertop tester that requires your alternator to be brought in hand to the store.

I think we should sticky this and add more about electronics and circuits, internal alternator workings etc. I know a fair amount from experience but this is just the start to the post and I wanted to keep it to the basics that make sense, also it just got to be a lot to type

 

If the charging light turns on, its actually more likely the alternator is bad, not the battery.

 

Thaaats a sort of truth, your very right, in most cases it is but technically its a charging system light with a picture of a battery.

 

Seriously, a sticky?
It's not even technically accurate.
Comment about battery
Voltages inconsistent with the FSM (which can be downloaded for free and has the proper diagnostic procedure)
Voltage- the electrical psi is that from an eight grade science book?

 

Lol.

 

Eighth grade science book, haha I like that.
Guess if you can get a free FSM and if what I wrote isn't "technically accurate" then its not helpful at all??
I could have been a lot more accurate, but its more general guidance I feel.
I'm not trying to come on here and say "sticky this because it's right" I'm saying its a good general help and that if it was to be a sticky, that ya know... more could come of it.

 

I now have a 03 Accord 4 cylinder. Yesterday, while driving, my battery light started flickering on and off randomly. I pulled over and went to get my battery and alternator tested at Advance Auto. The battery and alternator both passed the test, even with the light on inside the car.

I then continued my journey. Initially, it continued flickering on and off for about 20 minutes, but for the next 1 1/2 hr, it didnt come back on.

Is the signs of a 'dying' alternator? I have to take another 7 hr trip in the next 2 weeks. I do not want to be stranded, but I want to figure out the source of my problem.

On this same trip, my AC vent tube was clogged so bad that my entire passenger side was soaked with water, which went all the way to the rear of the car. I would not think this is related, but I figure it doesnt hurt to ask.

 

This is incorrect. On many fronts.
Describe how a shorted cell will cause a battery to explode.....
Completely wrong. The battery light on the dash does not indicate the batteries state of health.
This is mostly wrong.
12.2 static voltage is a bad/undercharged battery. I dont know where you got 14.4 volts from,but that number is irrelevant when testing a charging system. It is not that simple.
Misinformation should never be stickied.




Now, Im not trying to beat you up,but you really should do a little more research before posting a thread to consider for a sticky.

 

Possibly. The belt and belt tensioner should be checked first.