[Mocho213]

Hey guys, need help trying to figure out what needs to be replaced on this car. Recently bought it crashed and after looking into it looks like the BST cable fuse blew when crashed and the post melted. I will be replacing it with an OEM battery as existing battery is too small. As for the power distribution box do I need the box + cable. two photos shown below or just the box? I'm trying to figure out how the BST cable works and needs to be replaced? Any DIY steps or videos would be appreciated. Thanks for the help.

[Bavarian Tech]

The first photo is just your power distribution box. It should be okay assuming it isn't damaged. BST is the second photo, would be to be replaced to restore power to the starter. Once you remove the battery u can replace it with ease

[Mocho213]

Thanks, the power distribution box slightly melted with the fuse blowing, there's a top piece that basically broke off, so does the bst cable connect to the box or battery?

Steps going in would be new battery, power distributions, then the bst cable? I saw some talk of people crimping it together to a lead that runs to the fuse box, is this another issue/part?

[Bavarian Tech]

With such high amperage, I would replace both BST, a new power distribution and get a good proper size battery

[PhaseP]

Originally Posted by Mocho213

Steps going in would be new battery, power distributions, then the bst cable? I saw some talk of people crimping it together to a lead that runs to the fuse box, is this another issue/part?

New battery goes in. Then you connect the thin two wire BST ignition cable into the BST (you will see where it goes when you get it, on the not visible side of the picture you posted.) Then you place the BST on to the positive battery post and tighten it on the post with the nut on it that is half visible under the plastic lid, just like any other battery post connection. Then you place the power distribution box on top of the battery. The power distribution box will be connected on a stud/post that comes out of the BST, which is visible on your picture of BST, with a separe nut though. That makes the positive electrical connection to the distribution box. On your distribution box picture the hole that stud goes through is under plastic lid clip thing with a + sign on it.

You push the two stainless still side spring clips down on the battery they click and distribution box secures on top of the battery.

[PhaseP]

Also note yellow sticker that tells two times 15 Nm (11 ft-lb, 132 INCH pound) torque spec. This is for the distribution box to BST stud nut and also for the thick red cable that connects to the distribution box, under that other + sign at left lower corner.

It says two times, because those carry high current and if connection is not good and tight it will heat up.

The battery post torque, if the bolt is 6 mm, which most like will be, is 5 Nm (44 INCH pound (NOT foot pound!!))

[Mocho213]

Originally Posted by PhaseP

New battery goes in. Then you connect the thin two wire BST ignition cable into the BST (you will see where it goes when you get it, on the not visible side of the picture you posted.) Then you place the BST on to the positive battery post and tighten it on the post with the nut on it that is half visible under the plastic lid, just like any other battery post connection. Then you place the power distribution box on top of the battery. The power distribution box will be connected on a stud/post that comes out of the BST, which is visible on your picture of BST, with a separe nut though. That makes the positive electrical connection to the distribution box. On your distribution box picture the hole that stud goes through is under plastic lid clip thing with a + sign on it.

You push the two stainless still side spring clips down on the battery they click and distribution box secures on top of the battery.

Thanks! Really appreciate it, I seem to have it all figured out with all this info. Where does the cable coming out of the BST connect to though? The power distribution (fuse) box? Everything else makes sense, think a 90 Amp Exide battery, Group 48 should be fine? There's an 80 and 70 amp for slightly less but I will be upgrading some other things would that matter?

[PhaseP]

Sorry, I was thinking BST is already in the car ready. The thick cable from BST goes to a post on the bottom side wall inside the battery well in the trunk. From there it goes under the car to the front.
So first step would be connecting the BST cable inside the battery well. Then the rest.
In terms of length group 49 (H8) is the longest that can fit in there. You should code the new battery if you are putting in a different AH or type (AGM vs FLA) then original. If same just register with computer that it has new battery installed. Lots threads and info on battery replacement available .

[Mocho213]

Yeah I'm actually going to be replacing all three things so was wondering about the BST cable but makes sense now, thanks for the help and steps. As for the battery seems the information I had pulled up before means this is a good OEM replacement: 61217586962

[PhaseP]

For battery replacement, I would try to match these to the original:

- Type: AGM or Flooded Lead Acid (FLA) FLA will have liquid that can be heard to slosh around if shaken.

- Capacity: Best if you can match the RC spec. E90 original 90 AH FLA has RC of 160 minutes speced. That is what I had. If RC spec is not available, then match the AH spec.

- Size: My factory battery (90 AH RC 160) was size 49 (H8). Size 49 is the longest that fits in my sedan. The width and height also right at maximum. Anything smaller will also fit but have to match the capacity.

If you match the type and capacity, you only need to "register" the new battery to the computer. If you don't register car will still work, but supposedly computer will keep treating the battery as old and will charge it differently than a new battery. And computer may decide to cut off certain things earlier if you turn off the engine and keep the car on listening to music or running the fan etc. It may make the battery last less and blah blah..

If you change type and or capacity you need to "program (code)" the computer to know what the new type and capacity is.

From what you are describing and assuming you had FLA, your original battery was same as mine: size 49, 90 AH RC 160.

You can find many options as replacement. I have been using an AdvanceAuto branded one, which was speced RC 150. I had to replace it again after 4 years I think this winter a couple weeks ago. I bought again AdvanceAuto same part but this time got a "Made In Germany" sticker one on it. Doesn't matter much.

My 2nd battery started to die early because for at least a year I had been commuting very short distance, battery was hardly recharging at all.

BMW made this battery replacement way too complicated than it should have been.

[RecklessE90]

I know this is a old post I'm reviving but no one seems to reply to my post asking about something similar so hopefully someone on here will see this and reply to my post I just need an answer. https://www.e90post.com/forums/showthread.php?t=1968669