Well, you are on your 3rd battery, aren't you?
The 4th is due in 2011, 5yrs max. for panel batts. unless of course something is found to be wrong with one then it should be replaced earlier.
Alarm batts. are sealed batts. there are NO user (or Engineer) serviceable parts.
Alarm control panels DO have batteries. The one recommended for your panel is a 2.6 or 6Ah, don't think the 6Ah is available now so a 7Ah would be its replacement. In the case of an alarm the largest size that will fit in the panel will give the best standby time in the event of a power cut, it's supposed to be a minimum of 8hrs.
The above should be of help to you.
I'm not going to say anything much about your engineer, BUT words fail me, "When ordering a new battery was advised by expert (?) that panels do not have to have a battery, only the bell box." Get a NEW expert!!
Get back here with or for further information/help.
acorn
January 2011