2007 4.8i DOA...

[wsybert]

Sounds like a batt issue. I know AGMs are tough, but your symptoms seem to point that way. Im curious to see what the dealer says.

[PAX5]

Doing this from recall, but when you replace an old(er) battery, you need to tell the car's computer system that it there is now a "new" battery in the car (go to dealer). The reason behind this is that the computer is programmed to continuously update the output from the alternator over time as the battery ages. After about 4 years or so the alternator may now be putting out 20% to 30% more charge just to keep the weak battery at peak capacity.

If you don't reset the computer, the "new' battery will now be over charged because the alternator is still putting out the charge for an old(er) battery.

Overcharging can be disastrous to the sensitive electronics in the car over time. But I suspect that what might be happening in your case is that the system quit charging the battery and that you basically ran the car from a fully charged battery, until such time that the battery charge was used up again ...

Get the car reprogrammed at the dealer. Count on doing this every time you replace the battery (unfortunately).

[ard]

Originally Posted by basora

Doing this from recall, but when you replace an old(er) battery, you need to tell the car's computer system that it there is now a "new" battery in the car (go to dealer). The reason behind this is that the computer is programmed to continuously update the output from the alternator over time as the battery ages. After about 4 years or so the alternator may now be putting out 20% to 30% more charge just to keep the weak battery at peak capacity.

If you don't reset the computer, the "new' battery will now be over charged because the alternator is still putting out the charge for an old(er) battery.

Overcharging can be disastrous to the sensitive electronics in the car over time. But I suspect that what might be happening in your case is that the system quit charging the battery and that you basically ran the car from a fully charged battery, until such time that the battery charge was used up again ...

Get the car reprogrammed at the dealer. Count on doing this every time you replace the battery (unfortunately).

There is a simple 'registration' process ("programming") that can be done with any BMW computer... it is NOT as critical as your recollection suggests. It will only result in POTENTIALLY a shortened new battery life- like 25%. (IMO)...It should NOT cause this excessive drain or inability to charge/hold a charge.

[rcasey]

Ard, is this simple registration process something the DIY owner can do? If so, would you please elaborate?

TIA,
Dick

[Penguin]

Originally Posted by basora

Overcharging can be disastrous to the sensitive electronics in the car over time.

Please explain. I can understand how overcharging can shorten a battery's life, but can see no way this could damage any other electronics in the vehicle, since the voltage regulation always keeps the system voltage within the design range of the electronic components.

What is your source of this information?

[PAX5]

Originally Posted by Penguin

Please explain. I can understand how overcharging can shorten a battery's life, but can see no way this could damage any other electronics in the vehicle, since the voltage regulation always keeps the system voltage within the design range of the electronic components.

What is your source of this information?

It's current (amps) not voltage that causes damage. Much of the cars sensitive electronics draws micro-amps ... it doesn't take much.

I learned this in high school ... and from a close friend of mine who is a BMW master mechanic who has seen his share of BMW's get towed in because of fried electronics due to a lack of reprogramming the cars computer after replacing the battery ...