Delta TP Series Instruction Sheet page 8

 Battery Life and Precision of Calendar
Timer
Battery Life
Temperature (°C) -20 0 20 60
Life (Year) 1.972 2.466 2.712 2.835
Precision of Calendar Timer
1. At 0°C/32°F, less than -117 seconds error per month.
2. At 25°C/77°F, less than 52 seconds error per month.
3. At 55°C/131°F, less than -132 seconds error per month.