Screening use onlyResults are educational estimates. They are not verified for construction, equipment selection, or permit submission.· 1 registered heuristic group (H-007)Why

These calculators are undergoing a correctness audit against primary standards. Part of the logic still rests on engineering rules-of-thumb rather than rules traced to a dated edition of a code, and some published citations do not yet match the rule the code actually applies. Known defects are being fixed in sequence.

Treat every number here as a starting estimate to be checked, never as a design decision. Anything that will be built, energised, or submitted to an authority must be independently calculated and sealed by a licensed engineer who takes responsibility for the result.

Audit status: in progress · Assurance level: screening · Not for permit use

Rule-of-thumb decisions on this calculator

H-007 · screening only
Decision points: E24 part series assumed, selected upward from the calculated minimum · 2× resistor power-rating margin · 50% LED efficiency warning threshold · battery warning thresholds at 80% depth of discharge, 1C and one hour
Depth of discharge, system efficiency and duty cycle are now required rather than assumed, but LED and battery screening still assumes the available part series and a power-rating margin, and reports fixed warning thresholds instead of manufacturer operating limits.
Permit gate: block

Screening use only — Results are educational estimates. They are not verified for construction, equipment selection, or permit submission.

These calculators are undergoing a correctness audit against primary standards. Part of the logic still rests on engineering rules-of-thumb rather than rules traced to a dated edition of a code, and some published citations do not yet match the rule the code actually applies. Known defects are being fixed in sequence.

Treat every number here as a starting estimate to be checked, never as a design decision. Anything that will be built, energised, or submitted to an authority must be independently calculated and sealed by a licensed engineer who takes responsibility for the result.

Audit status: in progress · Assurance level: screening · Not for permit use

Rule-of-thumb decisions on this calculator

H-007 · screening only
Decision points: E24 part series assumed, selected upward from the calculated minimum · 2× resistor power-rating margin · 50% LED efficiency warning threshold · battery warning thresholds at 80% depth of discharge, 1C and one hour
Depth of discharge, system efficiency and duty cycle are now required rather than assumed, but LED and battery screening still assumes the available part series and a power-rating margin, and reports fixed warning thresholds instead of manufacturer operating limits.
Permit gate: block

CALC 05 · ELECTRONICSFREE

Battery Life Calculator

Runtime = (C × DOD × η) / (I × Duty)

BATTERY SPECIFICATIONS

Battery Capacity

Battery Type

Presets DOD and efficiency to typical values for the chemistry — adjust both sliders to your battery's datasheet.

Depth of Discharge

80%

System Efficiency

90%

Converter / regulator losses between battery and load. 100% = direct connection.

LOAD CHARACTERISTICS

Load Current

Duty Cycle

100%

Continuous

QUICK PRESETS

Typical catalogue figures as starting points — replace with the rating on your battery and the measured current of your load.

Common Batteries

Common Loads

CALCULATION SHEET

Total Runtime

18.0 hours

(18.0 hours)

Effective Capacity

1800 mAh

80% DOD × 90% efficiency

Average Draw

100.0 mA

(100% duty)

Days

0.8

C-Rate

0.04C

peak load current ÷ nominal capacity

Calculation Steps

01Battery capacity: 2500 mAh
02Load current: 100.0 mA
03Depth of discharge: 80%
04Step 1: Usable capacity = 2500 mAh × 0.8 = 2000.0 mAh
05Step 2: Effective capacity (90% system efficiency) = 2000.0 × 0.9 = 1800.0 mAh
06Step 3: Effective current (100% duty cycle) = 100.0 × 1 = 100.0 mA
07Step 4: Runtime = 1800.0 mAh ÷ 100.0 mA = 18.00 hours
08C-Rate: 100 mA / 2500 mAh = 0.040C
09Not modelled: self-discharge, Peukert/rate-dependent capacity loss, temperature — nominal capacity only

REFERENCE — BATTERY LIFE CONCEPTS

Depth of Discharge (DOD):

• Li-ion: 80-90% safe DOD
• Lead Acid: 50% max for longevity
• NiMH: 80-85% typical
• Alkaline: 80% usable

C-Rate:

• C/20 (0.05C): Very light load
• C/10 (0.1C): Light load
• C/5 (0.2C): Moderate
• 1C: Heavy (1hr discharge)
• >2C: Very heavy

Runtime Formula:

Runtime = (Capacity × DOD × η) / (Current × Duty)

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