Mr. Mark Lucas,
Did you look at the date of the posting you are responding to??
"Monday, February 13, 2017 at 12:54:46 AM"
By the time Greg, maybe read this posting, would place a key in the mail
in Victoria, Australia and for it to get to Zurich, Switzerland your
battery would be totally worthless, with your security at risk.
It would be easier, not to mention quicker, to just use a step drill
to bore out the lock and refit with a new lock.
Well on the other hand, call the local security dealer that might have
installed the system or not. They may have a spare key. :-)
Good Luck and Happy New Year!!
Les