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Changing Battery in the Key???

220K views 39 replies 21 participants last post by  Helsie99 
#1 ·
The battery is running low on my Mini key (2004 model) its becomming so bad that i have to stand next to the car to open it! I know how to open the key and change the battery. The question is: Will it still work after?
I have heard that you have to take it to the dealer to get the battery changed, because it "flashes" the key and it will no longer work on the car. Is this true? if so, how much will this cost?
I do have a spare key which works, but to be honest, its in perfect condition and i dont wanna use it unless i need to e.g. i lose the other key or something.
 
#2 ·
In theory the key shouldn't need the battery replacing; they recharge while they are in the ignition, though if you don't drive all that often it could slowly 'bleed' flat. If that is the case, use it manually in the door lock and it will recharge when it is in the ignition. Or you may have a bad battery and it just won't hold a charge. Do note that they don't work seem to work that well in some areas, those with lots of radio waves and other electronic interference. And if you don't use the spare key occasionally, it too will eventually bleed out.
 
#4 ·
Apparantly there have been several types of key battery fitted over the years.

To quote XRV848

The key was changed for the 2005 model year.
The 2004 owner's manual (USA) says:
"Replace (battery) if it is no longer possible to unlock the vehicle via the remote control...Only use a battery of the type specified on the battery, CR2032..."
The 2005 owner's manual says:
"In every master key there is an extended life battery that is charged automatically in the lock as you drive"
 
#6 ·
Time to re-open an old thread :D

I have an R56 MINI Cooper S race car. I've got the central locking working and the key will unlock / lock both doors but the remote buttons do absolutely nothing.

Yes, this should be the recharging type, and yes that means I shouldn't have to crack it open to change batteries, but as this one looks dead as a Dodo, does anyone know how to open the key? At least that way I can put a multimeter over it to see if the batt is dead or if there's other issues.
 
#7 ·
Well I have a 2003 Mini One D, it has a replacement battery, cos I had it confirmed by BMW, who also showed me how to get to the battery..

lever the cover off with a small screwdriver from the base of the key....

change the battery within 30 seconds... or you are in trouble...

put the cover back on and you are done...
 
#10 ·
Does anyone have URLs for where you can actually get a key battery as mini is dead dead dead. If I can whip the old one out and then whisk the new one in in under 30 seconds then that sounds good to me. Just don't know where to get one from.

Hi,

Any Maplin electronics will stock this battery , if you tell us the model and year of your mini we can tell you what battery to get
 
#15 ·
First generation keys:

'01-'04: Used a two button, clamshell shaped key. This key is easily opened with a flat blade screwdriver and the CR2032 battery is easily changed. This key is NOT recharged in the ignition switch. This is why it uses the CR2032 key, which is a 3 volt Lithium, non-rechargeable battery.

'05, '06 and some '07: Used a three button, flat shaped key. This key is sonically welded at the factory and not easily opened. I forget the number as I do not work on these keys but the battery is inductively charged by the ignition switch and not easily changed as it is soldered in place.

Val
 
#18 ·
There is a tutorial on here in one of the second generation forums about how to open your hockey puck style of key and replace the battery. I have done many first generation MINI key repairs and am now branching out into the second generation keys. I have new hockey puck shells on hand and am getting a supply of rechargeable batteries for these keys shortly.

I can't guarantee that a new battery will fix the problem a rechargeable battery that is left uncharged for a long time can go dead.

Let me know if you want me to work on your key.

Val
 
#19 ·
Actually to say, I have no experience about how to fix this case. The useful tips that I can give is about how to use 400w power inverter to charge camera battery. Simply connect this charger with car cigarette lighter charger outlet, then we can charge the tool you want safely. If you are interested in knowing more details about this charger, you can search bestekmall on Google. Wish this tip is helpful to you.
 
#20 ·
My 2005 mini one keys would start the car but wouldn’t open remotely with the key. I cut the 3 button key open carefully with a Stanley knife (it’s on YouTube) and unsoldered the battery - it has 2 soldered joints and is a rechargeable Panasonic ml2020 which are £3.79 on eBay. The old battery was reading 3.2 volts when tested but was still flat ( the voltage drops significantly when under load). The new battery was soldered in (try and be quick so as not to transfer too much heat to the circuit board). Unfortunately the new battery was flat when it arrived (about 2.5 volts). Once soldered onto the board I placed it onto my electric toothbrush charger overnight which brought it up to about 2.8 volts. Glued the key fob back together and used a little black sealant (mastic) to fill the groove id cut to open the key up and smoothed it over with a wet finger. Didn’t need to recode it and it worked perfectly and looks new. Why pay bmw £140 for a new key when a 4 quid battery and about half hours work fixed it. If you have any questions, please message me for info. Good luck!
 
#23 ·
Any one know if 2.80v is insufficient voltage for for key to not transmit unlock/lock and hatch open signal my key fob buttons don't work, this started after 2 incidents first my key ended up in the washer machine and still worked fine, the second incident I dropped the key and the key still worked fine, after ricing the key for a day it didn't work any more I just don't know if I broke it or if the voltage is to low I have to use the manuel key to open and lock right now. Tried fiddling with the circuit board while pressing buttons and for a little bit it responded but now the buttons don't do anything.
 
#26 ·
Didn't notice before but when I put the key in, the key battery symbol comes up for a few seconds on the tachometer when inserted into ignition. I drove probably like 5 miles when I noticed it but maybe it wasn't a long enough trip to get enough juice to atleast use the buttons once or twice?
 
#27 ·
you could try leaving the key in the dash over night if possible might find a long term charge will bring battery back failing that need to change the battery many battery's on ebay cheap need sharp blade to cut the plastic case open and solder gun/iron
 
#29 ·
Will the key battery charge if it's just clicked in ignition without pressing the start button? I drove around today to do some errands and buttons Still don't work, i opened up the key again to check the voltage and it's still at 2.80v when I press a button the voltage drops to 2.40v then comes back up to 2.80v when released as for how old the key is I'm not sure I only had this car about a month or two and it's the only one I got from previous owner, but it seems to me that the buttons do work mechanicaly but just not transmitting signal. Any good recommendation on where to buy a quality battery, also if I solder on a new one will I have to reprogram the key at the dealer?
 
#31 ·
Yeah so I just got the new battery in the mail and before I got into waisting my time soldering, I piggy backed the original battery on the circuit board with the new one wich had a charge of 3v and no response, I think its safe to say the key is busted, or some thing is wrong on the cars end of the recieving signal?
 
#32 ·
... I piggy backed the original battery on the circuit board with the new one which had a charge of 3v and no response, I think its safe to say the key is busted, or some thing is wrong on the cars end of the receiving signal?
Hmmm- quite possible, but also possible that by putting a good battery in parallel with a dud battery, that the dud is draining the good ones power.
You've got nothing to loose by properly attaching the new one (if it hasn't already been drained) - at least its easy enough to give it a quick recharge via a 5v usb supply
 
#33 ·
Yeah I'll give it a try later tonight but I honestly think the key is busted, because the first time I opened it up when it didn't work, I fiddled with the circuit board components applying slight pressure to solder joints and was able to make it work for like 5 seconds before it completely stopped responding to pressing buttons, and this was when the key battery was still at
2.70-80v. I just don't want to ruin the key completely cuz it's the only one I got right now, not really trying to buy a new one from the dealer.
 
#36 ·
Yeah I would have tried that unfortunately I didn't have one, thanks for the advice though 👍. Soldered in the new batt and know works. I'm going to open it back up again later after a few drives just to check that the key slot is charging because I was still getting the key battery symbol on the tach.
 
#35 ·
Just soldered in the new battery, and now the key works! Idk know the science or engineering behind it but at first it didn't work until I plugged the key into the ignition and pulled it back out to try the buttons again. I assumed that by piggy backing the old battery it would have worked so I was a bit doubtful but thanks guys for the advice. That's one issue down and out the way.
 
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