I don't think it is just the diesels that have had the battery problem.

Thanks for all the replies. I will remember to shut off the engine at longer stops but I think a traffic light won't be one of those situations.

Fair enough. I didn't recall reading much about this, but I don't have an E70. I did a search, and found one thread from 6 months back, another from 18 months back, and a series of SIBs from 2007 and 2008. Is it more widespread than that? Does your battery go flat frequently?

Onlt had mine for one month and 1300 miles. No problems so far.

BMWs bumpf for the current E70 states that, for fuel economy, the alternator is physically disengaged once the battery is fully charged. It also states that breaking energy is used to charge the battery; I am guessing via an auxillay alternator driven by the transmittion and electronically engaged when breaking ?

Maybe this system has teething problems?

There are couple of more threads on this general issue on bimmerfest. The number of threads is not very high. But several different people have posted that they have had a low battery problem in those threads. And the number of these problems which were reported to be SOLVED to the owner's satisfaction is almost zero*.

AFAIK ALL diesel engines put more load on a battery during starting, due to the higher torque required to turn over the engine and need to preheat the combustion chamber (glo plugs) when cold. The newer "clean diesel" engines add exhaust fluid processing: keeping the fluid from freezing and burning off the particulates. BUT in case anyone thinks this is just a recent US 35d teething problem, some of the reports are from Australia, and some are from gas engine models.

In my mind the real questions for people reading a thread is...
How many E70 X5s are running with batteries at a fairly low charge level but not low enough to trigger the iDrive warnings or cause the X5 to disable the starting system? And will shutting off their engine for short periods make their X5 one of them? :dunno:

Funf Dreisig

* At least one owner has reported getting BMW to install a larger 220 amp alternator as you suggested.

This is from the BMW Technology Site...

"BMW's Brake Energy Regeneration operates differently: the generator is activated only when you take your foot from the accelerator or apply the brake. The kinetic energy that would otherwise go to waste is now used efficiently, converted into electricity by the generator and stored in the battery."

Funf Dreisig

Ah Ha!

Quote
Today's vehicles require much more electrical energy than older models, due to the much wider array of electric and electronic on-board comfort and safety systems. This energy is created by the generator (also known as the alternator) which converts the engine's power output into electricity. In conventional systems, the generator is permanently driven by a belt connected to the engine.
BMW's Brake Energy Regeneration operates differently: the generator is activated only when you take your foot from the accelerator or apply the brake. The kinetic energy that would otherwise go to waste is now used efficiently, converted into electricity by the generator and stored in the battery.
Producing electricity in this highly efficient way delivers an additional advantage: when you apply the accelerator, the generator is deactivated - so the full power of the engine can be directed to the drive wheels. Brake Energy Regeneration thus increases fuel efficiency while simultaneously enhancing driving dynamics. As a safety precaution, the Brake Energy Regeneration system monitors the level of battery charge and will, if necessary, continue to charge the battery even during acceleration to prevent a complete discharging of the battery. end Quote



So these cars are running about with only just charged batteries it would seem.

London Lad......North American spec BMWs do not come with EfficientDynamics, which is the system that has Brake Regeneration. BMW needs to cut costs and our petrol is too cheap anyways to justify the additional expense of certifying the system.

Ah OK, just feel free to ignore me then :D