Although it's boring and going off topic I think it's important that when someone joins a thread and starts writing reams of information which is blatantly wrong, that it gets corrected, otherwise forum members may read and act on the erroneous information.

I have over 40 years experience in the auto electronics world and although ABMW obviously has some electrical knowledge he completely misunderstands the systems on a modern car.

Now for the last time (then I'm out of here)

1. There are NO capacitors in car starter motors on ANY car. There are also no capacitors in a cars starter system that "increase the amperage of the 12v battery"

2. Fitting a bigger (or extra) battery will NOT help a car start from cold IF the original problem was the battery is not getting fully charged. In fact it may make things worse as you will now be trying to charge two batteries when you were not running enough to even fully charge one.

3. No car will charge it's own battery enough to recover from a cold start in 10 minutes of running.

4. FWIW and IMHO only, I think that some of the problems that people are encountering with starting and low battery with modern BMWs are caused as follows:-

An alternator places a physical load on the engine; the more current you draw from it the harder it is to turn. For better fuel economy, once the battery is 'fully charged' modern BMWs disengage the alternator while the car is accelerating or hill climbing and re-engage it when decelerating or braking. Now, if BMW set the 'fully charged' point on the low side this will result in better fuel economy whereas if they set it a little on the high side it will result in slightly more starting capacity.

My guess is the point they have set works well for drivers in 'normal' climates who are reasonably conservative with the use of electrical consumers in the car, BUT for cold conditions and for drivers who are less careful about use of electrical consumers maybe the charge level is insufficient ?

My suggestion would be that drivers who are having battery problems first give their batteries a good overnight charge with a trickle charger / tender to ensure they are fully charged. Then ensure that they avoid switching on consumers such as lights or heated screens / seats etc until the engine is running and also make sure they are switched off before the engine is turned off.

The E70 has a massive amount of electronics on board and if you only do short runs then a trickle charger in the winter may be something you just have to live with.