[ggggbmw]

I started to get low battery warnings on my key fob, and I had to hold it on the 'magic spot' on the steering wheel to start the car, so I decided to replace the battery.

It was really simple, but I thought I would post a few pictures and tips to make it even simpler for the next person.

The battery is a CR2450. This is a huge coin battery. Way bigger than the 2032 used in most key fobs. These were likely original in mine, and my car had a 11/2013 build date. So, the battery should last quite a while.

The voltage on a new battery is a bit over 3.1V. The 'knee voltage' on these is about 2.9V. I think mine got a button pushed in a tight pocket when it was failing, as it recovered later in the day. It was reading a hair under 3.0V when I pulled it out.

To replace the battery, first pull the physical key out of the key fob. Then, using a tiny screwdriver or a small knife, insert it into the crack just below the left tab, and pry the cover off. Not in the hole where the key was, but in the tiny crack under the little tab. It's circled in yellow in this picture:


You could insert the screwdriver/knife under the right tab, but you get better leverage on the left, and you don't risk breaking the loop. Below is a picture showing the three tabs on the cover. The two on each side of the battery, with the yellow arrows, are the tension clips that hold the cover on. These are what you are prying against to get the cover off. The third tab, with the red arrow, holds the bottom edge of the cover in place.


The battery is held in place by a slight overhang of the case on one edge. It pops out with a nudge from the tiny screwdriver. This picture shows the slight catch where the yellow arrow points. There is also a little arrow molded in the case, in the yellow circle, showing which way to nudge the battery to pop it loose.


The new battery pops right in. Try to keep the battery clean as you put it in. Grease/gook on your fingers can be slightly conductive and cut into battery life if it bridges the +/- sides of the coin cell, or add resistance to the contacts. While the cover is off, blow dust off the inside, and be sure that the rubber seals are clean.

To reassemble, slide the cover bottom tab into the case, line the cover up, and give it a squeeze to pop it back on. The fob should just work. No resetting or registration of the battery/fob necessary.

[mdputnam]

An interesting side note. Yesterday I took my 2016 M235 in for its second Condition Based Service (i.e. oil change) and they replaced the FOB battery. Looking at the work order the task said,

"Replaced key FOB battery - every second oil change as per BMW recommended maintenance schedule"

That's a new one on me. I don't think they ever replaced the battery on our 2012 135i.

[pikcachu]

Originally Posted by ggggbmw

I started to get low battery warnings on my key fob, and I had to hold it on the 'magic spot' on the steering wheel to start the car, so I decided to replace the battery.

It was really simple, but I thought I would post a few pictures and tips to make it even simpler for the next person.

The battery is a CR2450. This is a huge coin battery. Way bigger than the 2032 used in most key fobs. These were likely original in mine, and my car had a 11/2013 build date. So, the battery should last quite a while.

The voltage on a new battery is a bit over 3.1V. The 'knee voltage' on these is about 2.9V. I think mine got a button pushed in a tight pocket when it was failing, as it recovered later in the day. It was reading a hair under 3.0V when I pulled it out.

To replace the battery, first pull the physical key out of the key fob. Then, using a tiny screwdriver or a small knife, insert it into the crack just below the left tab, and pry the cover off. Not in the hole where the key was, but in the tiny crack under the little tab. It's circled in yellow in this picture:
Attachment 1821763

You could insert the screwdriver/knife under the right tab, but you get better leverage on the left, and you don't risk breaking the loop. Below is a picture showing the three tabs on the cover. The two on each side of the battery, with the yellow arrows, are the tension clips that hold the cover on. These are what you are prying against to get the cover off. The third tab, with the red arrow, holds the bottom edge of the cover in place.
Attachment 1821764

The battery is held in place by a slight overhang of the case on one edge. It pops out with a nudge from the tiny screwdriver. This picture shows the slight catch where the yellow arrow points. There is also a little arrow molded in the case, in the yellow circle, showing which way to nudge the battery to pop it loose.
Attachment 1821767

The new battery pops right in. Try to keep the battery clean as you put it in. Grease/gook on your fingers can be slightly conductive and cut into battery life if it bridges the +/- sides of the coin cell, or add resistance to the contacts. While the cover is off, blow dust off the inside, and be sure that the rubber seals are clean.

To reassemble, slide the cover bottom tab into the case, line the cover up, and give it a squeeze to pop it back on. The fob should just work. No resetting or registration of the battery/fob necessary.

You don't really need a screwdriver or knife... the actual metal key fits right into the hole... to pry out the plastic...

those Germans think about everything

[Seba77W]

Good stuff.