Recommendation for float-service backup battery

Hi, I'd like a recommendation on specific makes / models of batteries for my long-term backup power needs for a fire/burglar alarm system.

Here are the specs & operating conditions:
12V, expected current draw max 2 to 3 Amps, only during power outages which occur ~3 times a year around these parts.
Desired capacity: 100+ amp-hours.
Charging: "dumb" constant trickle-charge from the alarm panel. 
Manual cycling/maintenance: I can arrange to deep-cycle the battery manually at recommended intervals but cannot physically access the battery for fancier maintenance such as hydrometer / fluid-level checking, etc.
Physical conditions: protected, dry space with average temperature of 50ºF to 75ºF average, occasional seasonal extremes of 40º to 95ºF. No vibration or harsh chemical vapor exposure.)

I think what I'm looking for is a "telephone service backup battery," designed for constant standby with low trickle charge, infrequent and moderate discharge rates. I would like to optimize for the longest-possible service life. I.e. I would rather pay $500 for a battery that will last for 15 or 20 years, vs. paying $150 for a battery that lasts only 3 to 5 years.