I am not a huge fan and rarely recommend wireless systems unless there is a firm business case that requires it. The maintenance issues can be significant, especially if the system has been poorly designed.

Temporary alarms and those in historic properties where running cables would be tricky would be two areas where I would recommend them. But you get nothing for nothing, and the cheap install savings can be outstripped by maintaining all those batteries.

I was once engaged in fire safety work for a NHS Mental Health Trust. A new building was built under a PFI arrangement . Part of the deal is the PFI company provided the (cheap to install) fire alarm system, but the trust had to maintain this expensive system - but only through the PFI company who added another mark up on the prices. If only the public knew how much was wasted and still is, under this system at this site!!

Hundreds of heads were installed in rooms constructed of dry lined stud walling, which was then beefed up with metal EML steel mesh sheeting to strengthen the wall in order to stop patients breaking through the plasterboard. The result? 100s of heads that were effectively screened from each other and could not transmit/receive a signal!! You couldn't make it up!!

As for giving you technical advice re batteries , try this forum where fire alarm installers meet. I am sure you will get good advise there

http://firealarmengineers.com/forum/index.php

Good luck!