[Solved] Huge power drain
Scotty, I have a 2013 BMW E88, Manual, 68k miles, and I'm having issues with the electical power in my car.
My start stop system still works which suggests the alternator is keeping the battery charged. I can leave my car for multiple days and the battery holds a charge however if the car is awake in any way, such as by opening a door, the battery drains insanely quickly. With engine off it can take about 20 minutes to drain the battery very low (to the point that modules start shutting down such as ABS, TPMS, roof control etc) just having the door open and no key in the ignition and it can drain in as quickly as 30 seconds to 5 minutes if the blower, stereo and headlights are on with accessory power and engine off.
Running the engine for a few minutes restores the modules back to normal.
Long time watcher on YouTube, thank you for everything you do!
Is there a way to see how much power is being demanded from the battery as I switch things on individually like headlights, stereo, blower/ac, dashcam etc?
Some vehicles actually track power usage. This live data would be available with a diagnostic tool.
most cars will have a main fuse.
Find the datasheet for your fuse.
Here is the data for the fuse in the example photo below: Littelfuse MEG100BP
Find the resistance. e.g. 0.56 mΩ
Switch your meter to the most sensitive voltage range (mV), and put the probes across the fuse. It helps to have a meter with interchangeable tips for this so you can use crocodile clips. Otherwise you might be able to squeeze your probes underneath the terminal. Do not use jumper wires. This will affect your reading.
Now monitor the voltage and use Ohm's law:
Let's say the voltage reads 1.1 mV. Using Ohm's law we get 1.1 / 0.56 = approx 2 amps of current
If you don't have a main fuse, or your meter isn't sensitive enough, you can use Scotty's method with a resistor.
But if your drain is really high as you say, then the resistor is going to get hot so be careful.
Sorry, forgot to update.
I pulled the battery, forgot to check for the date mainly because when I removed it I could see physical damage to the battery. It looked like it had been dropped on its bottom corner and it was clearly buckled. So I'm certain a cell was toast.
Bought a new Bosch S5A13.
Fitted it, coded it, registered it and now everything is perfect. Load tested it for quite a long time and it didn't even stutter.
Problem solved thanks for all the help from everyone!
In other news, since changinging the battery I'm now getting an intermittent misfire on Cylinder 4 so on to the next job of changing sparks, yey!
A battery and alternator load test will alert you to either needing replacement. Fixing either one might eliminate a future issue but that doesn't mean you don't have a parasitic drain on your system. So yeah, get a new battery, but continue on - troubleshoot just as you've planned.
Have you changed the battery recently? All batteries degrade over time. It may be time to change it. I had a 1994 BMW 540i 10 years ago, and that battery was last changed in 2006. I noticed it when the car was slow to start after a cold snap. It may start up fine, but it's only 3 or 4 seconds before the alternator kicks in. Sustained power is another story.
it can take about 20 minutes to drain the battery
That's a significant amount of power and the energy has to go somewhere. so, whatever it is probably gets pretty warm.
Is it possible that if/when the battery was changed at the dealership they didn't register/code the new battery? Would that cause these symptoms?
On a BMW, it wouldn't surprise me if there were some special procedure for battery installation.
But I don't think it would be the cause of a severe drain.