BMW 135i Battery Light is on Inspection at your home or office.

Common reasons for this to happen:

• Faulty or failed alternator: When the battery light comes on, chances are there’s not actually a problem with your battery. Usually it’s a problem with the system that keeps your battery charged. Many battery light issues center around the alternator, which is a generator used for converting mechanical energy into electrical energy. In short, the alternator takes the power that the vehicle’s crankshaft is generating, and converts that power into electrical energy, which it then sends to the battery. If your alternator is unable to produce an adequate amount of voltage, then the battery light will illuminate. When an alternator completely fails, your vehicle is entirely reliant on the battery for electrical energy, which means the car will soon stop running, as spark plugs rely on electrical energy.

• Bad voltage regulator: The voltage regulator is attached to the alternator and controls how much voltage the alternator is outputting. The voltage regulator limits the amount of voltage the alternator can send to the battery, and also increases the output when the extra voltage is needed. When this regulator breaks or malfunctions, the alternator no longer doles out the correct voltage into the electrical system.

• Worn-out serpentine belt: The serpentine belt – which helps drive not only the alternator, but also multiple other peripheral devices – can snap, which renders the alternator relatively useless.

• Corroded battery terminals or cables: While alternator-based issues are the main cause of the battery light coming on, it’s not completely uncommon for the triggering issue to reside in the battery itself. Just like with a battery in a remote, your car battery can die over time. Corrosion on the battery terminals or on the battery cables can also prohibit the battery’s ability to power the vehicle’s electrical unit.