which technique is better in using normal AA cells (for a wall clock or any device that draws low current) ?

If there are 3 (AA cells) of 1.5V each and if the wall clock or any other device that draws low current radio transistor or telephone (loud music melody ringer) and because of any weak cell(s) the loud music melody ringer doesnt ring then, what would be better technique :
1) Replace all three cells
2) Replace the one that is the weakest (by testing from Digital Multimeter, the lowest DC volts cell would be replaced).

thanks

If a remote stops working I rotate the batteries in place to clean the small contact areas. That usually keeps it going for a while longer. With multiples I do use a tester, but usually find that are all weak so I replace all. Replacing just one will mean you have to do it more often unless that one is considerably weaker and the others aren’t too bad.