What battery does a BMW Z4 key take?

BMW Z4 key battery

2009–2016

Smart keyVL2020
Not a battery you can swap. This key has a rechargeable cell soldered to the board, which charges while the key's in the car. A long drive can top up a weak one. If it won't hold a charge, an auto locksmith can replace the cell or the key.
Smart keyCR2032

How to change a smart key battery

Slide the release catch and pull out the emergency key blade.
Wrap the tip of a small flat screwdriver in tape or a cloth, put it in the slot the blade leaves and twist gently to part the case. Keep it off the circuit board and contacts.
Note which way up the old cell sits before you lift it out. It varies by key, so don't assume + is up.
Fit a new CR2032 the same way up, holding it by the edges. Leave any grease on the contacts.
Clip the case back together and test the buttons at the car. Most keys work straight away with no reprogramming.
Keep new and old cells away from children. A swallowed button battery can cause serious injury within two hours.

2002–2008

Remote head keyVL2020
Not a battery you can swap. This key has a rechargeable cell soldered to the board, which charges while the key's in the car. A long drive can top up a weak one. If it won't hold a charge, an auto locksmith can replace the cell or the key.

Questions

E89 (2009–2016): VL2020 in the smart key; CR2032 in the smart key. 1st generation (2002–2008): VL2020 in the remote head key.