Mini Cooper Key Fob Battery Replacement: CR2032 or Rechargeable, Which Key You Have and How to Open It

Mini key batteries confuse people because Mini, like its parent BMW, built two kinds of key for the same cars. One has a coin cell you swap in minutes. The other has a small rechargeable battery soldered to the board that tops up every time you drive, and if that one dies it usually means the car has sat for months or the cell has worn out after many years. This guide tells you which key you have, shows how to open the replaceable ones without marking the case, and covers how to start the car when the key is flat.

Which battery your Mini key fob takes

Find your key in the table. The quickest tell is the car: if there is a slot in the dash that the key pushes into, you have a slot-type key, and whether it is replaceable depends on whether the car has Comfort Access (keyless entry, where the doors unlock when you touch the handle).

The code tells you the size: the first two digits are the diameter in millimetres and the last two are the thickness in tenths of a millimetre, so a CR2032 is 20 mm wide and 3.2 mm thick while a CR2025 is the same width but thinner. A thinner cell in the same holder makes poor contact and causes the random dropouts people blame on the car. Our key fob battery size chart lists every size by brand.

What you need

Avoid rechargeable LIR2032 cells in a key designed for a CR2032. They have the right shape but a higher voltage, and they are not what the key is designed for. A branded 3 V lithium cell with a date well into the future is all you need.

Changing the battery in a 2014 or newer Mini key

This covers the current key with the emergency blade hidden inside, used on every Mini since the F56 Hardtop. It takes one CR2032.

If the rubber button pad lifted with the cover, lay it back in the body first, buttons facing out, and check it is sitting in its groove before you close the case. A pinched pad is why buttons feel mushy after a battery change.

Changing or recharging the battery in a 2007 to 2013 Mini slot key

The round slot-type key comes in two versions that look the same from the outside. Pull out the emergency blade (press the release on the back) and look at the slot it came from.

1. Comfort Access key: there is a small notch in the blade slot. Push the tip of the blade or a taped screwdriver in and twist; the back cover pops off and a CR2032 sits in a holder. Note which side faces up, lever the old cell out, press the new one in the same way round and snap the cover back on.
2. Standard key: the case is sealed and there is no notch. Inside is a rechargeable cell soldered to the board. It charges whenever the key is in the ignition slot with the engine running, and a flat one normally comes back after a drive of 30 minutes or more. Leave the key in the slot during the drive rather than taking it out at each stop.
3. If a standard key no longer holds charge after a long drive, the cell has worn out. Some locksmiths will open the case and solder in a new rechargeable cell; otherwise the fix is a new key from the dealer.
4. A first-generation 2002 to 2008 key works the same way as the standard slot key: it charges in the ignition and is not designed to be opened.

On both slot-type keys, the car reads the transponder through the slot, so even with a completely flat key the car still starts once the key is pushed in; you just have to unlock the door with the blade.

Do you need to reprogram a Mini key after a battery change?

No. The pairing between the key and the car is stored in memory that does not depend on the battery, so a Mini key keeps working as soon as a fresh cell goes in. If the instrument panel showed a key battery warning, it clears after the next start or two. If the key does not respond at first after a long time without power, hold it against the steering column marking described below for a few seconds; the car re-synchronises it.

If the car still does not see the key

First, get moving. On a 2007 to 2013 Mini, push the key into the slot in the dash as usual; the slot reads the chip and charges the key. On a 2014 and newer Mini, hold the key against the marked spot on the outside of the steering column, on the right-hand side below the stalk, press the brake and press Start; the car reads the chip through the column. The emergency blade opens the driver’s door if the remote lock does not respond; on the newer cars the lock cylinder is under a small cover on the handle that pops off with the blade tip.

Then work through the usual causes, in order of how often they turn out to be the problem:

• Wrong size. A CR2025 or CR2016 in a CR2032 holder makes patchy contact and the key works one day and not the next. Compare the code on the new cell with the old one.
• Upside down. If the key does nothing at all and the LED does not flash, open it and turn the battery over.
• Bent or dirty contact. The spring contact can be flattened by prying. Lift it gently with a plastic tool and clean it with a dry cotton bud. See how to clean key fob battery contacts.
• Tired new battery. Cells that sat in a drawer or came from an unbranded multi-pack can be flat out of the packet. Try a second one from a fresh pack.
• The car’s 12 V battery. If the car was also slow to crank or the dash lights were dim, the problem is the car, not the key. See can a bad car battery cause key fob problems.
• Damage inside the key. A key that has been dropped hard, through a wash, or left on a hot dashboard can have a cracked solder joint or corroded board. A locksmith can test whether it still transmits.

Mini keys share their electronics with BMW, so the fixes in BMW key fob not working apply. The general checklist is in key fob not working after a battery replacement.

What it costs

A Mini dealer will fit a battery while you wait, and many do it free for a car they service. The larger figures only apply if the key itself has to be replaced. Mini keys are ordered against the VIN and programmed with dealer tools, which is why a new one costs what it does, so it is worth keeping a working spare.

How long the new battery will last

A key without Comfort Access only transmits when you press a button, so a CR2032 in one typically lasts three years or more. A Comfort Access key listens for the car and answers whenever you touch a door handle, so expect one to two years, less if the key lives within a few metres of the car overnight. The rechargeable slot keys last as long as the car is driven regularly; a car that sits for months is what kills them. More detail is in how long key fob batteries last.