Do keys lose programming when the battery dies?

[Vince]

You are correct. All functions (Keyless entry, remote unlock / lock) all work as normal, no reprogramming needed.

It had been through the washing machine and it was sat in a drawer in pieces for months before I saw the thread and thought I’d ask.

Still should have come and played the wind up... what car... I never saw it

 

[Zaphan58]

Did you ever check or use the spare key fob to know if it ever did work ?

No idea if its ever worked. I just recently bought the car from my employer. They have had the car from new but the spare key has always lived in a draw at the office and not been used.

 

[mushtafa]

Most keys have two parts to them.
One for the remote locking, and another for starting.
The starting part is a physical coded chip within the key and will work even without a battery in the key. This is a read only chip and cannot be recoded.
The locking part requires the battery to operate and uses a rolling code for added security. If the key hasn't been used for too long or the battery has been flat for too long it can lose it's coding and will need resyncing to the vehicle.