Hi everyone, can anyone help I have 13.4v showing on my battery but the car will not start, this has happened a few times in the past few weeks and this time it won't even crank, a booster pack will not start it, the only way to get it started is using jump leads off a "running" car.

 

Let me get this correct.

Your car only start when you jump it from another car.

You won't get a crank or start with just using your battery to start.

At what point of the car are you testing your battery? I would test at the battery and the jump post. If testing at the front post and you're not getting the voltage you got from testing at the battery then you have a cable issue in the rear somewhere.

 

I have tested my battery at all points and yes I will only start when attached to another running car

 

You didn't respond to if it cranks with just your battery.

Also what year and more do you have

 

Sorry, no it doesn't crank with just the battery, just the ignition lights come on and nothing else, no warnings on the I drive either. Its a 2007 520d m47

 

Sounds exactly like the problem i had, did you try the jumpstart pack on the battery or the jumpstart points under the bonnet? Try this as an experiment, remove the battery and take it to the front and connect it to the jumpstart points with leads. Yes no battery in the boot for trial.

 

Check the voltage at the jump terminals in the engine bay. Compare to battery voltage in the boot. You say 13 v for the battery. That is suspect itself, since a resting battery doesn't usually show more than 12.6 v when fully charged.

 

I would say since it cranks with another car and doesn't with your battery there is an issue with your battery (how old is it) not enough power to turn over the starter, disconnected cable coming from the rear. Your battery definitely is too high without the car running.

Those are your only options since you can get the car started

 

Sounds like you got a bad battery. A bad cell most likely. That'd give you enough voltage but not enough CCA though.

 

Or, . . . . .you could just have a bad grounding strap between the chassis and the engine assembly (engine mount) which is why it only starts when jumped from another vehicle. When use the booster pack, try putting the grouns on the engine assembly. . . . . .