Originally posted by Aussiblue
Get a soldering iron, unsolder battery, take old battery to Jaycar, Altronics, Disk Smith or whoever to get matching replacement and solder back in; not hard at all.
Jaycar has the AA and AAA with solder tabs, ready to go for this purpose !
Mine uses 4 AA Batteries.
You could even use a Battery Holder, solder the connectors on to the siren board, and then replace the batteries yourself every 3 years without having to worry about soldering ever again.
(Although this depends on the size of the siren)