My key is starting to not work, doesn't always unlock my car, do I need to add some sort-of battery to it?

 

I see from your earlier posts that your MINI is 2005. Your key has a rechargeable battery that can go bad. Unfortunately the key wasn't designed for the battery to be replaceable — replacing it requires cutting open the case and unsoldering the old battery:
https://www.northamericanmotoring.co...key-issue.html

Do you have a second remote key (new cars came with 2) and does it work any better?

 

There are a ton of threads on dead or dying keys. DO NOT try to cheap out on ebay or otherwise. It will only bring you back for more advice.
The dealership needs a copy of your DL and registration, proof of ownership, which you can scan and email then they will let you know when you can pick up your key. The key will need to be initialized which you can do. Just ask for the directions at the service desk. You shouldn't pay any more than around $150 to $175. There are horror stories about some dealers wanting $300 or more. If it helps, I can PM you a scan of my dealer's invoice showing 165.95 including sales tax if they try to hi-ball you. The part number 66-12-6-931-749 is for a '06 R52 but shouldn't be that far off for yours.
Short of that, there's a guy on the forum who does rebuilds if that suits. He'll be in contact eventually. Good luck.

 

You make it sound like a bad thing that I troll for owners with key problems! I'm just trying to help others with my knowledge- I certainly don't make much on the key repair business.

To the OP- PM me if you want me to take a look at your key. Most repairs can be done for around $50. If you only have one key there is a cheaper option than the remote key- the "general, non-remote" key. They are right around $100 and allow you to use the blade to open the door and will also start the car. You should have a second key for anything you own, and your MINI is no exception.

Dr. Bruce Hart
MINI Key Hospital