Lately a lot of people have been complaining to me that the key no longer starts the car after replacing the battery. The battery is NOT needed to start the car. That is a completely different part of the key called the EWS and is comprised of a bar with ultra fine wire wrapped around it and a 8-pin chip (see #1 & 7 in the middle illustration at the bottom of this web page). If you nick the wire and break a strand, that's it, the key will no longer start the car! I can not be held responsible for damage to your key. These instructions are only a guide and you take full responsibility for any damage to the key or to yourself. I highly suggest not attempting this unless you have another key that starts the car so you don't turn the car into a hunk of metal stuck in the driveway until a new key is received from BMW.
If you don't feel comfortable doing the job yourself
you can send the key to me. I do BMW Key Fob Repair.
Note that I call it "Key Repair" instead of "Battery Replacement"
because most of the time the battery is just fine and the problem is a cracked
solder joint, bad button switch or some other bad component. Keys that are already
cut open will cost more to repair! Also I DO NOT repair keys that no longer
start the car. If the car doesn't start, it's time to buy a brand new key. I
have started a Key Fob Wall of Shame web page with
pictures of keys where a battery replacement was attempted. 1) First cut the key open. Use a utility knife
or xacto knife to cut. It will take many passes to get all the way through.
Be very careful not to cut yourself. Do not put the knife in too deep because
there are components inside near the edge of the board that can get knocked
off and destroyed. The picture below right is of a key that came in that the
customer had already attempted key repair and knocked off two components in
the RF section. One part was easy to replace because I know the value and I
have them in stock, but, the other component is an RF capacitor which has no
markings, can't be measured and are tuned to antenna. I have no idea what the
value it. I was able to repair this key, but, I charged him extra. For more
picture of dorked up keys visit my Key Fob Wall of Shame
2) Now that the key is open why not measure the
battery to see if it's really bad. Measure across the battery terminals shown
in the far right picture in step 4. A charged battery will measure between 3.1
and 3.3 Volts. I rarely find battery that don't take a charge and need to be
replaced. The new battery will measure between 2.95 and 3.00 Volts. This may
seem too low, but, it's fine because brand new batteries are not fully charged
from the factory. Once installed it may take 4+ hours of driving before it's
3) Below is a picture of the circuit board with
the original battery. Note how close to the board the battery is mounted especially
the battery terminal (see red arrow). The narrow terminal of the new battery
will need to be modified to be mounted this close. See pictures below of the
unmodified and modified battery terminal. I use a dremel tool with the composite
grinding disc. After modification add the adhesive pad if you bought the battery
and pad from me. Then cut off the other battery terminal approximately as shown.
4) Remove the old battery from the key fob circuit board.
Mount the new battery, to the board aligning the small battery terminal in the hole and
the edge of the battery very close to the wide battery terminal hole. Solder the narrow
terminal to the board. Then solder a wire from the end of the cut battery terminal to
the hole in the board as shown below. Never solder to the case of the battery itself.
5) Before glueing the key
back together test it with the car. You may need to perform the key
resync procedure to get the key to work since the battery was disconnected.
Test all the functions lock, unlock and trunk release and test at different
distances too. Once it tests out good glue it back together. I used to use cyanoacrylate
(super glue) to glue the key back together, but, I found it to be too brittle and it makes a mess inside.
After a few falls on a hard surface the case would pop open. Now I use a product called Amazing
GOOP Automotive adhesive in a red tube available from the auto parts stores.
Squeeze a good size drop onto a piece of paper and then use a toothpick to apply
it to both side of the key case. Reassembly the key and use a couple good rubber
bands to hold it together for a few days while it cures. Don't worry about the
excess glue that squeezes out. You can clean that up after it's done curing.
I sell the double sticky pad and VL2020 key fob battery used in the diamond key and in several other BMW keys since 2000. I sell them on eBay. My auction # is 270867834575
A lot of people have been contacting me about their BMW Key Fobs not working and want to replace the battery. I have worked on many keys and have only found one that needed a battery replacement because the battery would no longer take a charge. Most of the time the problem isn't the battery at all. It's a bad button switch, cracked solder joint, broken joint or the key just needs to be resync'd to the car. If you do attempt to do the battery replacement, be very careful opening the battery. You can very easily damage the electronics inside the fob and hurt yourself. Here is a guy that broke off a component E46Fanatics Forum post# 815604 If you don't feel comfortable doing the battery replacement yourself you can send your key in to me to have the work done. Contact me at firstname.lastname@example.org BMW key repair service.
Once the key fob is open the battery. You will want to replace the battery. I sell the same battery that BMW used, the Panasonic VL2020 Vanadium Pentoxide Lithium battery, but, the lead pattern is different. I've tried to get the correct one, but, it was a custom P/N for BMW which you cannot buy from Panasonic nor can you buy it from BMW. There are some sellers in China selling a CR2020 or DL2020 battery with the correct lead pattern, but, those batteries are primary batteries or in other words, non-rechargeable, one time use batteries that must not be charged. Since there is no easy way to disable the charging function in the key the charging current will damage the battery and shorten it's life. Other sellers are selling CR2032 batteries that they claim work in the BMW feb fobs, but, there are two problems. The 2032 is a thicker battery than the 2020. First two digits are the diameter and the last two digits are the thickness. A thicker battery won't fit well. The second problem is the battery chemistry. Most really aren't CR-type batteries. They are LIR-type Lithium ion batteries. What's the difference? Well VL-type are 3.0 Volt batteries which needs 3.4 ±0.15 Volts to charge. The LIR-type are 3.6 Volt batteries which needs 4.2 Volts to charge. The key won't generate a high enough voltage to charge the LIR-type battery resulting in a battery that is never really charged. Stick with the genuine VL2020 battery and do a little modification. Again I sell the correct battery either direct or through eBay my user ID is BMWGM5.
Left picture: 1 - Button for lock, 2 - Button for unlock, 3 - Button for trunk release,
Middle picture: 1 - EWS Transponder, 2 - Switch for trunk release, 3 - Switch for lock, 4 - quartz crystal, 5- Switch for unlock, 6 - Microprocessor, 7 - EWS pickup coil
Right picture: 1 - Rechargeable battery, Panasonic VL2020, 2 - Antenna
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