Battery Light
 

Hey all,

I have a 2005 4.8iS and while driving today the battery light came on. Then off a few minutes later. Then I started the car after 20 mins and it came on again while driving and stayed on until I turned the car off.

I'm getting a lot of mixed answers from searching. Some say alternator some say battery. As far as I know the battery is original. I'd rather replace the battery than the alternator!

I'll be going to Autozone to have the battery and the charging system checked today.

Anything else I should know about from anyone that's had this come up lately?

I think all the idiot lights on the car is covered in the owner manual.

Indeed, check the manual before paying for something that might be trivial. Could be a loose connection...?

If you have a multimeter lying around then pop the bonnet and check the voltage while car is running.

Manual says it's the alternator.

Some of the threads I was searching through say it's the battery however which confuses me. It's also on the original battery.

Have u tried to step on the throttle when u r parked when light is on? Do u have installed many things in the car? Like music! It could be alternator coils! Just one of the reason

Nothing is on, headlights are on auto, nav screen is always off, music was playing however.

I do not ask is everything switched on! When the light comes on try to step on throttle if it goes off should be coils..if I am writing that thing correctly in english! That thing in alternator!

I see what you're saying now.

I will try it soon.

I had with problem with Audi..I had installed music! Light came on regurally on traffic lights when music was on! Step on throttle and goes off!

I don't think it's going to work to be honest.

Anyone else had this happen to their X5?

Or you can unlock the OBC and check the voltage with the engine running.

Do you have a link for unlocking the OBC?

Have u checked connection with battery..is it strong? If u could check at home alternator..is it getting enough power while engine is working..

Have Autozone do the test, they may have to remove the battery and put a full charge on it to really test it. If you have a mutimeter check the voltage at the jumper terminals i the engine bay. Should read 14.5ish volts while running. Another easy way to check without a meter is to disconnect the negative battery cable at the battery while running. If the engine falters or stalls out, it's the alternator. This can be dangerous, so don't do it if you're not confident.

Just unlocked the OBC (really easy lol) to see what my battery voltage was while parked and off.

It read 11.3V.

I'm positive this is the original battery haha.

That's a little low, may have a bad cell or it's not being fully charged back up by the alternator. You need to check the voltage while running. I just went through all this a few month ago. Good luck

Thanks man, what did your car eventually need? I started my car and the battery light came on about 2 minutes later haha

well, mine was part of diagnosing an intermittent no start issue. My battery was also showing only about 11.5V after charging and testing at the local auto parts place. I did replace it because it was the original battery. I also tested the alternator at the parts place and with a multi meter at home. It showed about 14.5V under load, that's with the lights on and heater blowing, radio on, etc. So I never had a battery light on. It's been my experience with other cars that the battery light does indicate a bad alternator. But you really need to do some solid testing to make sure. Especially with these cars, the parts are expensive and the alternator is difficult to get at. The battery is the cheapest, easiest thing to replace but it may not solve your problem. Do more testing.

One last thing, an aftermarket battery is fine. But if you buy an alternator make sure it's BMW or the OEM manufacturer. Find the part on line BMW Parts Catalog then shop around.

11.3 is a little low???

11.9 v is 0% charge status!

11.3 is deader then dead.

Measuring State-of-charge - Battery University

Many BMW owners replace @ 50% (12.2v).

Yea I'm stranded on the side of the highway right now.

200% sure it's the original battery haha

Holy cow, you are driving a car with fault lights actively on, and they are telling you that the electrical system is on the fritz, yet you drive anyhow?! That's the definition of insane. You should commit crimes, and point to this as a defense for your actions.

The BATTERY LIGHT is not a battery light at all, it is a CHARGING SYSTEM light. It _always- means that the alternator is not producing sufficient electricity to maintain vehicle operations, and that the vehicle is operating off of battery power. It will operate fine, until the battery is dead. You know it is dead when non-essential systems, such as the radio and the AC systems shut off as the car tries to keep enough power to keep the engine running.

I was driving in my F150 several years ago and the "battery light" came on. I thought I had about 30-ish minutes of operation before the truck shut down, and it was about 5 minutes to my destination, and 10 to 15 minutes home. I guessed wrong. Within a minute or two, the gauges on the dashboard stopped working and the radio switched itself off. I was able to make it to the right lane so I could park at the curb, but once the charging system failed, it was not long before the battery was toast. I assume a fresh battery might last longer than an old one. When I took the alternator out, one of the two brushes inside was worn down to a nub, and it was not capable of collecting electrical current from the stator.

An alternator makes AC current. There is a voltage regulator -- bridge rectifier circuit -- that converts the AC to DC so that the vehicle systems can use it. Some cars used to have generators that made DC current, but the industry has gone with alternators instead of generators. I do not know the reason why. Perhaps an alternator is cheaper to build, even with the cost of the voltage regulator added on.

The charging system light can mean that the alternator itself has failed, or that the voltage regulator has failed. Some cars allow the VR to be replaced separately from the entire alternator -- BMW is among them. You can buy the VR for less than half the cost of the entire alternator. An alternator is a far better buy as a new part as opposed to a rebuilt one.

Alternator can charge the battery when the engine is at idle, whereas the engine has to be spinning at a higher RPM in order for the generator to charge the battery. Both Alternator and generator utilize voltage regulators.

Hello,

My X's battery light is on and off since couple days ago. it is intermittent. Even when driving on the freeway, it can be on and off and on.

I check the battery terminal under the hood, when Engine is off, the battery is 12.59 to 12.61 volt and when Engine is on, it is 14.16 to 14.18 volt. However, the voltage sometime drop 12.XX to 13.XX for flash of moment and up. Not sure if it is my hand not holding the meter contact sturdy or its the alternator not stable. I try to make my hand sturdy for about 20 seconds and it is stable @ 14.17 Volt.

Any advise is appreciated.

Thanks
Leon

It was my alternator. Was also stupid expensive. I'm sorry.

You may as well replace the battery if it original. If it's that old and has been drained that much it probably doesn't have much life left.

Thanks for the advise. the battery is less than 2 years old. when engine is off the battery still have 12.6 Volt when connected to terminals. When engine is on and idle, the battery has 14.17 Volt. Not sure if it is really the alternator going out.

The battery light is not constantly ON. and goes off and on time to time. Truck starts up fine everyday and drives normal.

Lessons learned the hard way are always hard on the humans and the one paying for the repair. Take a few mins and read the DIY articles on the forum and do a little search on ownership issues and solutions here on the forum. It will make you a prepared owner.
Enjoy your X5.

Isn't that what the owner's manual said about the battery light?

Driving around with a bad battery probably also hasten the death of your alternator. An alternator is not meant to charge a DEAD battery. People that jump a car and then drive around hoping that the alternator will recharge the battery is only killing the alternator. An alternator is only designed to maintain the voltage in a battery. If the battery is dead, you are better off connecting a battery charger and let the battery charger recharge the battery.

The battery light is really a Charging System light. When on, it means that the alternator is not working correctly, or at all. When the charging system light is on, the car is operating off of battery power. This means you should turn off everything that you can turn off else risk the battery giving out before you can get to a safe place.

The job of the battery is to start the engine. Period. After the engine is started, all electrical loads are provided for by the alternator. If the charging system light is on while the engine is running, it means that the alternator is on the fritz. You could have a failure in the alternator or the voltage regulator, or a faulty connection. You need to diagnose the charging system, not the battery. You can have a battery in poor conditions, and if the charging system works right then the car will run fine and the light will not be on. Depending on the condition of the battery, the car will run for anywhere from a couple of minutes to somewhere more than an hour with the charging system light illuminated.

Thank you guys, yea, it is the alternator. When the light is on, it was only 11.9 Volt. Truck is in my indy shop now. He charges $250 for labor, $425 for the alternator (Bosch or $7XX for a OEM one so I just picked the Bosch), $50 for antifreeze and $6 for the o-ring. total about $730.

Every time I work on the car, my wife buys me a USDA Prime Rib Eye steak with the money that did not go to the shop for the $450 part, plus $250 to bolt it on. Holy crap! Your mechanic should take you on a ride on his yacht since you are the one making the payments.

Holy crap, when I rebuilt the alternator for my X, I just brought a Valeo voltage regulator and did the job in a couple of hours. Total cost was 60 bucks. You guys must be rich.