[windy1603]

Was the new battery a Duracell. I have heard some people have had issues with them due to the bitex coating they put on them causing a poor connection. Cleaning with Alcohol or nail varnish remover can sometimes get them working

 

[windy1603]

Another thing to check (if the key is the same style as the DS5 Keyless one) its very easy to push the negative tab into the fob as it's connects to the side of the battery and if it gets pushed down it does not connect I fixed it on my DS5 by pulling it back up and hooking it over the edge of the battery