03 525i battery dead only when it's cold outside.

[bmw440]

Only when it's cold, battery drains that it won't start. A few hours to overnight. Has anyone had issues where your heated mirrors come on when it's cold ? I touched the driver mirror and it was warm.i gave my bimmer a boost and started right up. I unplugged all radio,heater fuses even the famous FSU plug.

[edjack]

Is the car going to sleep?

How old is the battery?

What are your commute miles?

What was the battery voltage before you jumped it?

Did you put a charger on the battery after the jump?

[StephenVA]

This might help you. Posting once again

Test Starting and Charging systems:
Test Battery with Volt meter at the battery terminals
Reading with car off READS XX.x Volts (12.6V+ good) If under, charge for 12 hrs using a harry home owner charger (5- 25 amps) Afterwards: Does the battery read 12.6+V? Yes go to next step
Place a 50% battery amp capacity amp draw on battery for 15 seconds. Don't have a carbon pile tester? Turn on every accessory the car has for 30 secs with engine off (fan on HIGH). This will get you close.
Read voltage: Over 12.5 V? No throw battery in trash
•The time needed to charge a completely discharged battery can be estimated by using the reserve capacity rating of the battery in minutes divided by the charging rate.
•Hours needed to charge the battery = Reserve capacity ÷ Charge current
•A battery load test loads the battery to one-half of its CCA rating. A good battery should be able to maintain higher than 9.6 volts for the entire 15-second test period

Check charging systems
with Volt meter on the battery posts read total voltage at idle, 1500 and 2500 rpm, Over 14V?

BMW Vehicle Parasitic Draw Testing
When your car battery goes dead overnight, usually either the battery is at the end of its life span, or you left something on, such as a light. Occasionally something is drawing power that's not of your doing. This is a parasitic draw, and it can cause the same result as leaving the headlights on: a dead battery in the morning.

1. Remove the negative side battery cable from the negative battery terminal.
2. Connect the black wire to the com input on the multimeter and the red wire to the 10A or 20A input on the multimeter. The meter needs to be able to read at least a 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won't work and could damage the meter.
3. Attach a multimeter (set the dial on the multimeter to measure Amps as per multimeter instructions) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".
4. If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
5. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings) last. Perform the same steps for relays found in the fuse panel. Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.
6. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners' manual or service manual to find what circuits are on that fuse.
7. Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
8. Repeat steps 1 & 2 to test your repair. The ammeter will tell you the exact numbers.

Need more? http://www.bimmerfest.com/forums/sho...d.php?t=510579

Helpful?

[Qsilver7]

The heated side mirrors are operating parameters is a specific on/off cycle that's based on the ambient temperature. This helps with condensation that can form in some climatic conditions where the glass is cold but the weather is cold & humid...or other odd conditions where condensation can suddenly appear due to weather conditions (other than snow/ice/freezing temps).

Back in Feb...there had been snow on the ground...then overnight the temps went up into the 40s. When I was parked in the garage everything was fine, but as soon as I backed out of the garage...the humidity of the melting snow and temps that had risen quickly above freezing caused the windows to immediately fog up when I backed out into the drive. In conditions like this, the side mirrors also fogged over, but the heating elements started clearing them immediately.