Lifetime of battery depends from many things, charging voltage should be minimum float charge voltage at 13,5V-13,8V (@25C and reduce each 18mV per one C if temp is above 25C) and can go to 14,2V-14,4V cycling recharge voltage, and most important thing is charging current, for that small battery should be around 0,2A but check manufacturer battery datasheet.
Better use LM317 to limit current.
Its very bad for lead acid battery to stay in empty or below full voltage (12,72V-12,73V), specialy for longer time, and its very bad to discharge it completely, sulfatisation can occure. That small lead acid have around 200 cycles, if you discharge it 100% each time, 400 cycles if you discharge it 60%, around 1000 cycles at 30% discharge level, but check manufacturer datasheet, and expected lifetime is 3-5 years. Capacities of this small lead acid batteries are often declared in C/20 current-time.
Maybe is better solution to use NiMh battery. You can get 12V from 10 NiMh cells or 13,2V from 11 NiMh cells. But you can use AA 3000mAh-3500mAh (3Ah-3,5Ah), or smaller AAA 1200mAh-2000mAh (1,2Ah-2Ah).
Here is one battery datasheet 12V 1,2Ah as example :
**broken link removed**
I have to admit that I've never heard for this company. I take first result from Google search. :smile: