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.