HELP! Parasitic Battery Drain After Accident
 

Hi everyone,

It’s been awhile since I’ve last logged on but was wondering if any of you can help me. My X5 was involved in a rear end accident, airbags did not deploy but the impact was enough to explode the BST. I’ve since replaced the BST/positive cable with a new one and now I’m running into what seems like a parasitic draw.

Some back story, before the accident, I bought a new Interstate AGM battery (same exact model) that replaced the dying battery. 2 weeks after installing the new battery, my mom gets rear ended and the car won’t start due to the BST. Car was towed to the yard and when my dad went to pick up the vehicle, the car was completely dead, no power whatsoever. Which is weird because 1) the battery is only a few weeks old and 2) the forums and YouTube videos said I should still have acc power even with a blown BST. So I thought the battery must’ve been damaged due to the force sustained upon impact. So I went ahead and purchased another new battery and 2 weeks later, I go to start the car and the crank was weak. Figured it was due to the car sitting. Drove the car around after replacing the front control arms, everything was good just needs an alignment now. Thursday on the 3rd week since instal comes and my dad tells me the car is completely dead again.


I’m currently charging the battery and will check if it will hold charge. Will also try to run tests to try and locate where this draw is coming from. Would any of you happen to know what could potentially be causing the draw after an accident? Is there a module or safety sensor I had to replace after the BST explodes? I feel like I could be going down the rabbit hole trying to find the culprit and want to possibly avoid that if possible if someone has knowledge of what could be going on.

HELP! Parasitic Battery Drain After Accident
 

Start with the FSU is the #1 culprit. Does the car have comfort access? That's a common killer also. There are about three more common culprits.

Any chance they have a phone charger plugged in? My e53s had always on 12v sockets.

Put it to sleep mode. Do a voltage drop across fuses. You'll find the culprit faster. Latch the door, upper hatch, and tape the hood switch so it will go to sleep. Fuses will be easier to reach.
Is everything working properly?

When you renewed the battery did you check the vehicle is charging properly?

No shortcuts. There are several sources of a parasitic drain. you must diagnose it.

Set up a multimeter - I actually use 2 - one for measuring Mili-amps on negative terminal and one to measure mili-volts across fuses.

Get the car in sleep mode with tailgate and glovebox/fuse tray open.
Don't test fuses by pulling them...measure mili-volts across back.

Check my posts if you want to see the process described.

Thanks for all the replies. I’m currently having the battery charged and if the current one holds charge will put it back in the car and run the tests and will report back. Hopefully I’ll be able to find it to avoid having to bring it to the shop.

From what I know everything works as it should radio, nav screen, etc. only thing illuminated on the dash is the airbag light after start up. I know the NAV cd player can’t read the disc anymore for some reason, I wonder if that is the culprit and the draw began before the accident.

Will check the FSU, but it was replaced a few years ago with a new one so not sure if it should fail already.

+1

I support that line of reasoning. There's a chart for mV per Amp per each ampacity fuse rating. Start on the HVAC blower fuse. FSU still the most common parasitic drain.

Update: Went ahead and did the test with the multimeter and while I was waiting for the car to sleep, I noticed the rear map light was on. Restarted the process to let the car sleep and did not find any draw from the car. Battery has been recharged and has a charge that’s over 12v when car is off. Drove the car around the block and the vehicle charge is 13.6-13.7 while driving.

Started the car multiple times and no issue so far. Will continue to monitor but I think the culprit was the rear map light.

The rear map lite should go off when car goes to sleep.