Step-by-step walkthrough
Use this companion guide beside the interactive calculator to make sure you understand the “why” behind every click. Each section includes the classroom explanation, student-friendly language, and quick practice prompts.
Collect the data points listed below and double-check their units. Keeping an organized “givens” list is one of the fastest ways to reduce math errors and impress exam graders.
Step 1
Find the battery's rated capacity in mAh (check the label or datasheet).
Step 2
Estimate your average load current — for variable loads, use the average draw over a typical session, not the peak.
Step 3
Set depth of discharge and efficiency conservatively (80% DoD and 85–90% efficiency are reasonable defaults for lithium packs) rather than assuming ideal conditions.
That gives an optimistic, best-case number. Real batteries lose usable capacity at higher discharge rates (Peukert effect) and rarely run to full depletion, so scaling by DoD and efficiency gives an estimate closer to what you'll actually see.
Use a time-weighted average. If it draws 500mA for half the time and 50mA idle for the other half, enter roughly 275mA rather than either extreme.
