Electronics
Battery Life Calculator
Enter the battery's rated capacity, your device's average current draw, and how deep you plan to discharge it to estimate runtime in hours and days.
Estimate runtime from battery capacity, load current, and how deep you plan to discharge it.
Runtime from capacity and load
t = (Capacity × DoD × η) / I_load
Usable capacity is the rated capacity scaled by depth of discharge (DoD, since most batteries shouldn't be run to 0%) and system efficiency (η, to account for converter or regulator losses). Dividing usable capacity by the load current gives runtime.
How to use
- Find the battery's rated capacity in mAh (check the label or datasheet).
- Estimate your average load current — for variable loads, use the average draw over a typical session, not the peak.
- Set depth of discharge and efficiency conservatively (80% DoD and 85–90% efficiency are reasonable defaults for lithium packs) rather than assuming ideal conditions.
Example
Input: 2000mAh battery, 250mA load, 80% DoD, 90% efficiency
Output: ≈ 5.76 hours of runtime
Student-friendly breakdown
This walkthrough emphasizes the most searched ideas for Battery Life Calculator: battery life calculator, battery runtime calculator, mah to hours calculator, how long will my battery last calculator. Start with the formula above, then follow the guided steps to double-check your work. For quick revision, highlight the givens, plug into the equation, and finish by verifying your units.
Need more support? Use the links below to open the long-form guide, browse additional examples, or hop into adjacent calculators within the same topic — each one is a quick way to double-check your work or handle a related question without starting from scratch.
Deep dive & study plan
Battery Life Calculator: Estimates runtime from battery capacity, load current, and discharge depth. It's built around battery life calculator, battery runtime, mah to hours, so you can go from a raw question to a checked answer without switching tools.
The math behind it: Usable capacity is the rated capacity scaled by depth of discharge (DoD, since most batteries shouldn't be run to 0%) and system efficiency (η, to account for converter or regulator losses). Dividing usable capacity by the load current gives runtime. The core relationship is t = (Capacity × DoD × η) / I_load, shown above the calculator so you can see exactly how your inputs turn into the result.
To use it well: (1) Find the battery's rated capacity in mAh (check the label or datasheet). (2) Estimate your average load current — for variable loads, use the average draw over a typical session, not the peak. (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. Keep your units consistent as you go, and re-run a case you already know the answer to — it's the fastest way to catch a typo before it throws off a result you're relying on.
Worked example: entering 2000mAh battery, 250mA load, 80% DoD, 90% efficiency returns ≈ 5.76 hours of runtime. Try swapping in your own numbers next, especially a case you're unsure about, before you use this for something that matters.
Quick retention checklist
- Speak the formula aloud (or annotate it) so the relationships stick.
- Write each step in your own words and compare with the numbered list above.
- Swap in new numbers for the Example to make sure the calculator (and your logic) handles edge cases.
- Check at least one related calculator below — it's the fastest way to confirm your numbers still line up from a different angle.
FAQ & notes
Why not just divide capacity by current directly?
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.
My device's current draw isn't constant — what should I enter?
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.
What formula does the Battery Life Calculator use?
Usable capacity is the rated capacity scaled by depth of discharge (DoD, since most batteries shouldn't be run to 0%) and system efficiency (η, to account for converter or regulator losses). Dividing usable capacity by the load current gives runtime.
How do I use the Battery Life Calculator?
Find the battery's rated capacity in mAh (check the label or datasheet). Estimate your average load current — for variable loads, use the average draw over a typical session, not the peak. Set depth of discharge and efficiency conservatively (80% DoD and 85–90% efficiency are reasonable defaults for lithium packs) rather than assuming ideal conditions.