Red Battery Light Came On Randomly

Last night when I was leaving work, after I had turned on my car, the red alternator light stayed on for a few seconds longer than all the other lights, but then it shut off. So I start driving, and a few minutes into my drive, I'm cruising at not much faster than 30 MPH and the light comes on again for no reason... no power loss, all electronics working, no other warning lights on, and the red light turns off after a few seconds. Comes back on again for a few seconds, and nothing. And that was the end of that for the rest of the 25-mile ride home through both streets and highway.

The reason why this freaked me out is because my alternator already died 6 months ago (<10,000 miles) and was replaced by a good mechanic with a new Bosch one, so I don't really think it's the alternator going bad, but I would probably cry if I had to shell out so much money again. Could it be some connections I'd have to check?

Any help would be appreciated. Thank you.

iwas going to say alternator, but after reading, maybe your mech didn't completely tighten up some wires?

you need to test your voltage....to see if you need a new battery or alternator

Make sure the wires are tightly connected to your battery terminals. A place like AutoZone can check the battery charge for free, but make sure they give it a minute or two... had to replace mine after about 5 years. Otherwise it's likely to be an alternator problem. I had mine replaced this past year, except my cluster lit up like the 4th of July with warnings when it first went off. After a quick on/off, the only thing remaining lit was the red battery.

I'm going to try the voltage test tomorrow guys and I'll post the results here. I thought you actually needed an external voltimeter to do that hah.

Anything that comes up red is bad and needs to be checked immediately. Battery light coming on would mean check either your battery or terminals, or connections somewhere.

I just did a voltage test and it read 12.1-12.2 before starting and 13.9 with the engine on, which, as far as I know, is pretty normal. The light came on again this morning after starting my car and turned off for a moment and then came back on again. I shut off my car, checked the battery connections to see if everything was okay, and then started the car up again -- no lights came on.

What the heck is going on???

I want to say it sounds like a break in the rotor of the alternator. It happen to me a while back and it cost me 50 bucks to get a replacement rotor and I was back on the road. Loose wire wont be affected by the speed of the motor, besides if anything was loose you would burn the plastic coating off with a quickness. Because of the resistance and the amount of power the car requires to be functional.

Originally Posted by CrisB02

I want to say it sounds like a break in the rotor of the alternator. It happen to me a while back and it cost me 50 bucks to get a replacement rotor and I was back on the road. Loose wire wont be affected by the speed of the motor, besides if anything was loose you would burn the plastic coating off with a quickness. Because of the resistance and the amount of power the car requires to be functional.

You think if I go back to the mechanic who installed the alternator he would check for this? I have no experience with working with the alternator so I don't know how else to check the rotor.

I still have the original battery that came in the car from the factory. It is in perfect working condition.

Could be the Water Pump/Alternator pulley is going out, that happened to me on a previous E46.

Take it back to the mechanic and explain to him what is going on. How long ago did you replace the alt?

It's going to sound weird but, the power steering reservoir is on top of the alternator, just as precaution, check IF there is any leak in the hose and this oil is going inside the alternator, this is going to kill it, that happen to me and the solution was to buy a can of circuit cleaner and with the battery disconnected spray liberaly inside the alternator, is going to dry really fast, after that replace the power steering hose (return) and voila!, no more issues with my alternator.
By the way, is a good idea to cover your alternator with a shield to prevent future leaks going into the opening of the alternatror; i'm working in that and I'll be posting some pictures soon.

Im pretty sure the red lamp indicates alternator output low or internal (alternator) regulator fail.

My wife's MINI just ate a battery which shares the "battery" indicator which never came on. The circuit does not monitor battery voltage, just charging status. The international icon should be an alternator but no one would get it. Our old cars displayed "alt" or "gen" remember? Your alt should be under warr.

I don't know too much about alternator problems with these cars but I would assume if your voltage goes up one the car is running then that means the alternator is still functioning. My red battery light just came on today and when I tested the voltage it is at 12 something before I start it, and then once it's running drops down the 11.4. to 11.5. bad news for me i guess...

I drive an 01 BMW 325i, i was driving to school today and the red battery light turned on half way to the school, it turned off then turned back on after a few seconds, i got nervous because have never seen that before, and turned off the a.c and rolled down the windows after turning off radio and everything electrical, then when i got to the school and turned off the car it would not turn back on and would just click like if the battery was dead.. My battery had died about two weeks ago now that i think about it, then all of the cluster lit up, i am going to go check the battery in a bit.

The Battery Light is really a Charging System Light, and it means the alternator has stopped working. It does not mean the battery is giving you trouble.

Your battery is dead because the alternator is not charging it up anymore. You might still have a serviceable battery, but until the alternator comes back online there is no way to tell. Well, you could take the battery to the store for testing, but even if the battery is good, the charging system is still toast. You need an alternator. More accurately, you need a voltage regulator.


THIS POST IS IN REPLY TO POST #16. THE THREAD WAS REVIVED.

You either have a problem with your belts, or alternator, or wiring. Run it too long that way you might also end up with a battery problem. Red lights mean you have a problem that needs to be fixed. Often this just means your alternator needs new brushes - they are carbon and wear out.

Take it to the mechanic and have them check the alternator and belts...
If it just got installed 6 months ago, it should still be under warranty...

Don't waste too much time with that, it can lead to other electrical problems while you are driving...

If I were you, I would take the car to a third party shop and have them do the test on the alternator and battery... Just to see what they say, compared to just going back to the shop where they install your current alternator.

Good luck...

Say what? If the belts were broken, the report would be that the car overheats. The belt (there is only one that goes to the alternator) cannot be the problem in the absence of overheating. It is absolutely true that the broken belt will turn on the alternator light (charging system light), but if this was the case then the car would also overheat very quickly.