BMW is not alone here, a lot of brands have issues when vehicles are not driven far enough to charge the battery. There have been a huge surge in adding in electronic features that all suck down power. The alternators have not increased in capacity to match. BMW went a more complicated route but getting 4.5 years out of a battery is about what you would expect. Ford, GM, Chrysler ll have had battery issues as well. There are many modules in the car and they all take power and they usually have an awake and a sleep mode. When they are awake, they take more power and it can be 30 to 45 minutes before they go to sleep. The battery a car has today is not much different than the battery they had over 20 years ago.

I think a 48-volt system will help things. You can use thinner wires as they can handle the same wattage compared to a 12 volt system. Say you need 48 watts on a 12 volt system. That would be 4 amps and would require a 15 AWG wire. On a 48 volt system, that would only be 1 amp and a 21 AWG wire can be used. A 48 volt system could help reduce power requirements; the hybrids aren't using 12-volts motors.

Another factor that has caused this; more gears. We have had four speeds for ages and then 5 speeds came around, then 6 speeds and not long after 7 to 10 speed transmissions. The reasoning has been better fuel mileage and how do you get better fuel mileage with more gears? Reduce the RPM while driving. In the city and not going fast enough for top gear; you will still find an 8 speed allowing lower RPM's than say a 6 speed. On the highway, you will find an 8 speed allows lower RPM's for going the same speed. Lower RPM's means lower alternator output since it to is spinning slower. Add more electronics in a vehicle that want power and you have to drive farther to replace what was consumed by the starter and the electronic while it was off.

The N63 has a 230 amp alternator. The N62 has an 180 amp alternator. Both of those ratings would be at 2500 RPM or higher. I can be in top gear and run at around 1000 to 1100 RPM doing around 45 to 50. On a 6 speed, that would be about 1300 RPM. To go 70 MPH; it is 1900 RPM on an 8 speed and 2100 RPM on a 6 speed. So while the alternator is larger, it has to be because the engine is spinning slower to do the same amount of work.

There are many factors why people are seeing battery issues now compared to earlier vehicles.