The calculation
planned active hours = active days × hours per day
full-charge equivalents = ceil(planned active hours ÷ usable runtime)
session equivalents = ceil(hours per day ÷ usable runtime)
Worked example
A 4.5-hour test with a 20% reserve gives 3.6 planning hours per charge. Six seven-hour sessions require 42 active hours: 12 full-charge equivalents across the project, with 2 equivalents available for each seven-hour session.
Start with a relevant runtime
Use a timed test made in the same capture mode, interval, display and accessory setup. A photo-count rating or continuous-video rating may describe different conditions. If the camera manual publishes time-lapse recording time, use the matching mode and note the stated temperature and settings.
What a charge equivalent means
The result is an energy-planning unit: one equivalent is the usable runtime you entered for one fully charged battery. It does not tell you how many physical batteries to buy. That depends on how long each pack takes to recharge, whether you can swap it safely and whether the camera can use external power while shooting.
Allow for the real schedule
This calculation assumes each active day has the same shooting hours and that the camera draws no battery power outside those windows. Standby, cold weather, screen use, autofocus, long exposures and connected accessories can change endurance. Increase the reserve or repeat the test when those conditions differ.
Keep the original test duration with the camera mode, interval, temperature, battery age and accessories. Nikon notes that endurance varies with battery condition, temperature, interval and menu display time. The test record makes the input easier to revisit when one of those conditions changes.
Common questions
Does the result count physical batteries?
No. It counts full-charge equivalents. The number of physical packs depends on recharge time, swap timing, and whether the same pack can be reused between sessions.
Can I use the camera’s maximum battery output rating?
No. Use a measured runtime or a manufacturer estimate for your actual time-lapse mode. A maximum output rating is not a runtime measurement.
Should I include overnight idle time?
Only if your camera or power system draws from the battery while idle. This simple planner counts the active hours you enter and assumes no off-session draw.
Further reading
Official or original references for the workflow; these organizations do not endorse this independent tool.