It depends on your CPU model and how often you conduct regular inspection.
The backup time after a battery error is detected is as follows.
NP1PS-32/32R: Approx. 230 hours (Approx. 9 days)
　NP1PS-74/74R/117/117R: Approx. 140 hours (Approx. 5 days)
　NP1PS-245R: Approx. 80 hours (Approx. 3 days)
　SPH2000/3000 all models: Approx. 230 hours (Approx. 9 days)
　SPH200 all models: Approx. 230 hours (Approx. 9 days)
For example, if the regular inspection frequency is half of the 'backup time after a battery error is detected,' you should replace the battery within half of the 'backup time after a battery error is detected.'
The above backup times are for when the ambient temperature of the PLC is at 25℃.
Considering that the backup times are reduced by about half for every 10°C increase in ambient temperature, determine how often to conduct regular inspection and when to replace the battery.
If the regular inspection frequency is longer than the 'backup time after a battery error is detected,' you need to replace the battery immediately.