This is a normal symptom of a dead battery, the OP has a charging system light that's on. His battery will start the car today, but soon it will be dead too. The charging light means the alternator is on the fritz.

The cheapest thing to do is to use a set of jumper cables to start the car, then the charging system (alternator) should be able to charge the battery IF the battery is able to accept a charge. If the charging system light is on, then the battery is not the problem, the alternator is.

This is in case you need an alt Dab

Hard to argue with a lifetime warranty
https://www.fcpeuro.com/products/bmw...tor-x5-al9413x

All the alternator does is charge the battery. It doesn't power the electrical system.

Um, not correct, the alternator is responsible for powering everything in the vehicle and it also can charge the battery. That being said, depending on how the vehicle is used, often the battery does not get properly charged.

But BMW's and most modern vehicles can go haywire when the cranking Voltage drops too low and the many modules fail to properly communicate. Very strange things happen with low batteries and unstable charging systems in modern vehicles.

The alternator replenishes battery voltage at a rate exceeding draw on the battery keeping the battery at a little over 12v. The alternator does not provide power directly to anything. All systems draw the power needed to run them from the battery.

You are absolutely wrong about this and I have no idea where you learned anything about automotive charging systems. Automotive charging systems in basic theory have not changed significantly for over 100 years. In the past 20 years there have been some variations to how the systems work, but the primary purpose of the battery is to start the engine as well as stabilize and filter the charging system, which powers the vehicle electrically components. Why do you think that majority of alternators today are typically between 120 and 200 Amp? When was the last time you say a battery charged at 120+ Amps?

There are a few vehicles that are designed to draw from the battery as a fuel saving measure, but this is only under very controlled situations. My GMC truck does occasionally draw directly from the battery and some of the Mazda Skyactive systems do some similar things. But again, these are very specific situations and the alternator does kick back in to handle the bulk of the electrical load on the vehicle.

Let me ask this basic question, IF a fully charged Lead/Acid battery has a terminal Voltage of 12.6 Volts, why do you find the majority of the vehicles operating at 13.5-14.5 Volts? Where do you think this additional power is coming from?

Maybe you are confusing where power connections are made, this is a very different story and a power connection is not necessarily the source of the energy.

I just do not understand how people can think this is accurate information.

So did you have any formal Automotive Training?
Did you ever make a living repairing vehicles?
Were you ever a Certified Mechanic?

If the answer was yes to any of the above, you must have not been aware of anything you did on a daily basis.

While your symptoms sound like an alternator issue I would not buy anything yet.

When you get it home remove the battery cables and clean the posts and the connector. Then charge the battery. If after the battery has been charged your X won't start then have the battery load tested to verify if it is good or bad.

Once the battery is charged or a new one installed unlock the cluster. Read the battery voltage using the cluster. Start it up and read the alternator output.

The reason I am suggesting this process is there are other possible causes for your problem that are unconnected to the battery or the alternator. Best practice is to spend the time to troubleshoot to find the root cause before buying parts.

The the failure of an alternator does not mean the battery is also bad. The failure of a battery does not mean the alternator is going to fail. The life cycles are different.