Why doesn't my BMW's Efficient Dynamics system work for short journeys?

The AutoStop/Start on my 2009 BMW 120 M Sport stopped operating on a journey from Bromley, Kent to Cornwall. On return from holiday, 500 miles later, I booked the car into my BMW dealer. I was told my driving profile showed a majority of short runs and that the battery was low, and that they would keep it on charge for the day. On collecting the car I was told that the AutoStop/Start would start operating again once the car had been "put to bed for at least five hours". It was also suggested that I invest in a trickle charger. Also it was mentioned that this problem occurs all the time with BMWs.

Needless to say the problem has not been rectified and the car returns to the workshop next week for two days. It seems odd to me that the battery is not charged after 500 miles covered in two journeys and I am told that the battery will drain even on long journeys. So why are short trips blamed for the problem if long trips make no difference?

Asked on 7 December 2013 by JB, Bromley

Answered by Honest John
BMW Efficient Dynamics only works if the car is driven distances. If you don't drive distances you chose the wrong car. It has a special type of battery that is charged on engine overrun. If the battery is not regularly kept fully charged it loses its capacity to hold a full charge. So if you keep the car you do need a "battery conditioning trickle charger". Or you need to drive the car a lot further.
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