Just ask parts staff to find out if the service guys try that.
Unless you feffo know the correct code of the battery that belongs in there! (Assuming the old was one was the correct one.)
There might be variations of key fobs too so havig your chassis or reg handy will help them find out which one was issued and the correct battery(s) and how many fit/needed for the fob.
Then go to Maplins etc and find a cheap replacement instead of £4 at Halfrauds.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150338834789&viewitem=
Once you change out the battery, you may have to reprogram the remote.
307 PLIP PROGRAMMING
1. Turn the Ignition switch to the ON position using the first key.
2. Press the LOCK button for 10 seconds.
3. Remove the key and wait for 10 seconds.
4. Check the Plip key operation.
5. Repeat for second Plip key if required.
6. Turn the ignition OFF