This does not factor in Free Rescue Notifications.

Batteries consumes 3 Rescue Notifications, and gives you an Auto-Rescue. Below shows how you can get the best value for each item.

Going exclusively off of initial item quality

Stopwatches are the best, having an item quality of 2, giving 1 more Battery each than Lure (the other item with a quality of 2), and giving 2.5 times the number that Alarm Clocks (the one with a quality of 1) gives you. The Calendar gives 12. However, due to its item quality of 4, they are too valuable to turn into Batteries.

Going exclusively off of notification number

Calendars are the best, as Calendars have 1 more than 2 times the amount of Rescue Notifications gained as a Stopwatch, but 2.4 times the number of Batteries per item.

Based on Murphy’s working time, Stopwatches are the best for lower-quality items giving 5 Batteries per 8 hours, and Calendars are the best overall.

Conclusion

The best rate all depends on how you use them. If you are using them for auto-rescues, 1 auto-rescue per Lure equates to 4 auto-rescues per 12 notifications. Exchanging Lures for Batteries and using 2 Alarm Clocks per Lure exchanged gets you the most value out of each item, getting you 4 auto-rescues each time. However, if you aren’t, and are just stockpiling Batteries for no reason (when doomsday arrives), Stopwatches are the best.