[soursamo]

Car was sitting for a few months over the winter while I did my water pump, so wasn't too shocked to find the battery dead.
Got a new one yesterday, installed, car wouldn't start?
Saw a few posts about the IBS possibly being the cause, so pulled the blue cable out of the distribution block and the car started right up!

Turned off, plugged it back in, car ran fine. Went out for a drive last night, no issues.

Cut to this morning and it's dead again; lights on the dash and a click when I try to start?
Pulled the IBS cable again but no luck.
What should I check next?

[robthewrench]

Check the battery voltage at the battery. Should be 12.6V for the new battery. If even a 0.1 less, you have a drained battery. Charge the battery, see if the car starts. After this, you'll need to figure out why the battery is draining.

[soursamo]

Found the airbag style plug on the back of the positive terminal was loose.
Put that back on, car fired right up.

But now it's dead again and won't start.
Will grab a meter tonight and see what is causing the draw.

[gabylonfive]

Originally Posted by soursamo

Found the airbag style plug on the back of the positive terminal was loose.
Put that back on, car fired right up.

But now it's dead again and won't start.
Will grab a meter tonight and see what is causing the draw.

That's the BST connector (battery safety terminal), and it's known to cause a bunch of problems if it gets kinked or comes loose. I've seen it cause draw issues and airbag lights if its on its way out. I was working on an e92 with a faulty BST connection and we had to plug a 2 ohm resistor in-line to get the car to fire up. Weird fix but it worked to at least get the car out of the garage.

[soursamo]

Originally Posted by gabylonfive

That's the BST connector (battery safety terminal), and it's known to cause a bunch of problems if it gets kinked or comes loose. I've seen it cause draw issues and airbag lights if its on its way out. I was working on an e92 with a faulty BST connection and we had to plug a 2 ohm resistor in-line to get the car to fire up. Weird fix but it worked to at least get the car out of the garage.

Problem ended up being corroded positive cable at the bottom of the battery box: literally fell apart when rechecking it. Cut off gross end, new ring terminal and cleaned up the posts.
Fixed

[Three_thirty_I]

Originally Posted by gabylonfive

That's the BST connector (battery safety terminal), and it's known to cause a bunch of problems if it gets kinked or comes loose. I've seen it cause draw issues and airbag lights if its on its way out. I was working on an e92 with a faulty BST connection and we had to plug a 2 ohm resistor in-line to get the car to fire up. Weird fix but it worked to at least get the car out of the garage.

That's interesting! Can this be intermittent, as in cause a draw issue sometimes, but not always? My E90 has an intermittent power drain that is killing the virtually new battery. The old battery was only two years old but did have a dead cell, but the problem is definitely a power drain. I have been monitoring the battery voltage from the engine bay jumper points, and about a week ago I caught it doing this. But my main suspicious is that one of the door locks is causing this power drain, and when I unlocked all doors, opened all windows, then closed again but unlocked the driver's door, it was fine again and the battery voltage recovered to a higher value than before, meaning that there was less power being drawn from the battery. And these tests were all done about an hour later so that the electronics had chance to go to sleep mode. Is there a way to easily test these door locks and determine which one is faulty? Most likely the driver's door, but interestingly BMW had replaced it without telling me back in 2012 under motorplan...

[soursamo]

Originally Posted by Three_thirty_I

That's interesting! Can this be intermittent, as in cause a draw issue sometimes, but not always? My E90 has an intermittent power drain that is killing the virtually new battery. The old battery was only two years old but did have a dead cell, but the problem is definitely a power drain. I have been monitoring the battery voltage from the engine bay jumper points, and about a week ago I caught it doing this. But my main suspicious is that one of the door locks is causing this power drain, and when I unlocked all doors, opened all windows, then closed again but unlocked the driver's door, it was fine again and the battery voltage recovered to a higher value than before, meaning that there was less power being drawn from the battery. And these tests were all done about an hour later so that the electronics had chance to go to sleep mode. Is there a way to easily test these door locks and determine which one is faulty? Most likely the driver's door, but interestingly BMW had replaced it without telling me back in 2012 under motorplan...

I would definitely pull the battery and check the posts, here's what mine looked like:

View post on imgur.com

[Three_thirty_I]

Originally Posted by soursamo

I would definitely pull the battery and check the posts, here's what mine looked like:

View post on imgur.com

I will have to check, but I highly doubt that mine are corroded, and the auto electrician that fitted and registered the new batteries in the past would have pointed this out. But anything is possible.