DBS keyfob battery replacement
Discussion
Sorry Ross, I cannot answer your question, but might be able to help with searching this forum.
I use the Google search and type something along these lines.
pistonheads forum - Aston Martin - owners who have bought more than one car
That method even helped me to find topics written back in 2003, talking about the new Vantage, when unveiled at the North America Auto Show.
If you put site:_pistonheads.com then a space and your search term into Google it will only search the website after the site: expression (remove the underscore - I added this to stop the forum displaying an emoji 
I used this and the search term site:_pistonheads.com reprogram aston martin glass key (no underscore) and found multiple threads. This one
https://www.pistonheads.com/gassing/topic.asp?t=17...
seemed to have something similar to what you’re experiencing. One quote in particular:
The plan originally was to have three fully functioning keys. Coding the second glass key to start the car is easy. You start the car with your first key, then you start it with your second key, then you start it with your new key. All in ten seconds or so. Despite fully expecting the new key to do precisely nothing, I was surprised to find that this works. So now I had three keys that start the car.
However, the new key would *only* start the car, and wouldn’t unlock or lock it. A call to the AM dealer disclosed the importance of the key code. An AM dealer can code a key to lock and unlock your car if you have the key code that came with the key. Otherwise no go.
There is also a link to a sixspeed thread that I didn’t open that might be of help
I used this and the search term site:_pistonheads.com reprogram aston martin glass key (no underscore) and found multiple threads. This one
https://www.pistonheads.com/gassing/topic.asp?t=17...
seemed to have something similar to what you’re experiencing. One quote in particular:
The plan originally was to have three fully functioning keys. Coding the second glass key to start the car is easy. You start the car with your first key, then you start it with your second key, then you start it with your new key. All in ten seconds or so. Despite fully expecting the new key to do precisely nothing, I was surprised to find that this works. So now I had three keys that start the car.
However, the new key would *only* start the car, and wouldn’t unlock or lock it. A call to the AM dealer disclosed the importance of the key code. An AM dealer can code a key to lock and unlock your car if you have the key code that came with the key. Otherwise no go.
There is also a link to a sixspeed thread that I didn’t open that might be of help
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