When the battery back-up becomes weak, the Smoke Alarm will “chirp” about once a minute (the low battery warning). This warning should last 30 days, but you should replace the battery immediately to continue your protection.

Internet research learns that a typical life cycle for the back-up battery in the de BRK Smoke Alarm  7010BE as used in a environment and configuration like the Warande building,  generally does not exceed  3-4 years.  To prevent low battery warning during night hours or other periods  when not prepared for replacing it, the recommendation of your residents’ committee is to replace it at least every 3 years.

Make sure you use a fresh alkaline battery for replacement preferably still  5 years  away from its expiration date and hasn’t been sitting on the shelf for a couple of years. 

Always discharge the branch circuit before servicing a mains (AC) or AC/DC Smoke Alarm or to replace a battery. First, turn off the mains (AC) power at the fuse box. Next, remove the battery from the Smoke Alarm. Finally, press and hold the Test/Silence button for 5-10 seconds to discharge the branch circuit.

https://www.youtube.com/watch?v=z6oOz1AYk7Y instruction to replace battery step 2 thru 7