CALCULATORS / BATTERIES AND ENERGY STORAGE

Battery runtime calculator

Energy budget; usable fraction and load are assumed constants

batteries-runtime.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	energyWh	runtimeh
	192	3.2
	192	1.92

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

runtime requirement3.20 h✓ passes

BASELINE INPUTS

voltage24 V1248capacity10 Ah220usable0.8 load60 W20150

CALCULATED

energy192 Wh

runtime3.2 h

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Energy budget; usable fraction and load are assumed constants
voltage = 24 V in 12..48
capacity = 10 Ah in 2..20
usable = 0.8 "Assumed usable capacity fraction"
load = 60 W in 20..150
energy := voltage * capacity * usable [Wh]
runtime := energy / load [h]
check runtime requirement: runtime >= 2 h
scenario high load: load = 100 W

Calculated from your source · not saved

Baseline · Baseline

runtime requirement3.20 h ✓ passes

high load · high load

runtime requirement1.92 h × fails

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

energy: energy = voltage * capacity * usable [Wh]
runtime: runtime = energy / load [h]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

voltage: 24 V
capacity: 10 Ah
usable: 0.8
load: 60 W

Calculated

energy: 192 Wh
runtime: 3.2 h

Assumptions and limits

Energy budget; usable fraction and load are assumed constants

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Battery runtime. Inputs: usable capacity; voltage or discharge curve; load profile; efficiency. Outputs: runtime range; reserve allowance. Model scope: Cell/pack data and stated electrical and thermal conditions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: usable capacity, voltage or discharge curve, load profile, efficiency
Outputs: runtime range, reserve allowance
Modes: calculate, compare, sweep
Drawing: Pack and energy-budget plot

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS