Battery Runtime Calculator
Enter rated capacity, then select unit: mAh, Ah, or Wh
Lead-acid: 50%. Li-ion: 80%. LiFePO4: 90%.
Account for inverter/DC-DC converter losses (typically 85–95%)
Used for the ProgressRing — how long do you need it to last?
Enter Battery Details
Select a mode, enter your battery capacity and load, then see how long your battery will last — with energy breakdown and scenario comparison.
How to Use the Battery Runtime Calculator
Choose Your Mode
Select Standard for everyday batteries (phone, laptop, power bank, UPS), Peukert for lead-acid batteries (car, marine, solar), or IoT / Duty Cycle for microcontrollers and embedded sensors like ESP32 or Arduino.
Enter Battery and Load Values
In Standard mode, enter your battery capacity (mAh, Ah, or Wh) and your device load (W or A). Use the chemistry preset buttons to auto-fill DoD and efficiency for your battery type. Use device presets to quickly set common load values.
Adjust DoD and Efficiency
Slide the Depth of Discharge to reflect how deeply you plan to cycle the battery — 50% for flooded lead-acid, 80% for Li-ion, 90% for LiFePO4. Adjust efficiency for your inverter or DC-DC converter losses (typically 85–95%).
Read Results and Compare Scenarios
The hero value shows your runtime in hours (or days/years for IoT). The energy breakdown bar shows usable energy vs. DoD reserve vs. efficiency loss. The scenario table compares runtime at 25%, 50%, 75%, and 100% of your entered load so you can plan for different usage intensities.
Frequently Asked Questions
Why does my actual battery runtime differ from the calculated estimate?
Several real-world factors reduce actual runtime below the theoretical estimate. Temperature is the biggest variable — cold weather (below 0°C) can reduce lithium battery capacity by 20–50%, and lead-acid performance degrades even faster. Battery age also plays a major role: a battery at 200 cycles may deliver only 80% of its original capacity. Peukert effect in lead-acid batteries means high discharge rates reduce available capacity significantly. Variable loads (motors, backlights, radios) cause current spikes that the calculator cannot model. For safety margins, add 20–30% extra capacity over the calculated runtime requirement when sizing a battery for critical applications.
What is Depth of Discharge (DoD) and why does it matter?
Depth of Discharge (DoD) is the percentage of a battery's rated capacity that is discharged before recharging. Using more of a battery's capacity per cycle reduces its total cycle life significantly. Lead-acid batteries discharged below 50% DoD can suffer permanent sulfation damage and may lose 30–50% of their total cycle life. Lithium-ion batteries are more tolerant but still benefit from shallower cycles — keeping lithium cells between 20% and 80% state of charge can extend cycle life from 500 cycles to over 1,500 cycles. LiFePO4 batteries are the most tolerant and are commonly discharged to 90% DoD without significant cycle life penalties.
When should I use Peukert mode vs. Standard mode?
Use Peukert mode for flooded lead-acid, AGM, or gel batteries, especially when the discharge current is high relative to the battery's rated capacity (C-rate above 0.1C). The Peukert effect is most pronounced for flooded lead-acid batteries discharging at 0.2C or higher — for example, a 100Ah battery at 20A (0.2C). At this rate, the actual runtime can be 20–30% shorter than simple division predicts. For lithium-ion and LiFePO4 batteries, the Peukert exponent is so close to 1.0 that the correction is negligible, and Standard mode is perfectly adequate. AGM and Gel fall between these extremes.
How do I estimate runtime for an ESP32 or Arduino IoT sensor?
Use IoT / Duty Cycle mode. Measure or look up your device's active current (ESP32 during Wi-Fi transmission draws about 240 mA; during CPU-active processing about 50–80 mA). Enter the deep sleep current (ESP32 deep sleep draws about 10 µA = 0.01 mA). Set the active time percentage — for a sensor that wakes every 10 minutes and takes 5 seconds to transmit, the active fraction is 5 / (10×60) = 0.8%. Enter your battery capacity in mAh. The calculator computes weighted average current and projects runtime in days or years. A 2,000 mAh battery powering an ESP32 at 0.8% duty cycle with 0.01 mA sleep current can last well over a year.
What does the C-rate mean in the results?
C-rate is the discharge current expressed as a multiple of the battery's rated capacity. A 100 Ah battery discharged at 10 A has a C-rate of 0.1C — meaning it would discharge in 10 hours at that rate. A C-rate of 1C would discharge the same battery in 1 hour (100 A). C-rate matters because high C-rates cause greater internal heating, accelerated aging, and (for lead-acid) stronger Peukert effect. Lithium batteries can typically handle 1C to 2C continuous discharge without performance issues. Lead-acid batteries are most efficient at low C-rates (0.05C to 0.1C). Very high C-rates (above 1C for lead-acid) significantly reduce delivered capacity and should be avoided for longevity.
What is the 15% aging deration option?
The aging deration checkbox applies a 15% reduction to your entered battery capacity before calculating runtime. This accounts for capacity fade in batteries that have completed many charge-discharge cycles. A new 100 Ah battery might deliver 98 Ah in practice, but after 500 cycles it may only deliver 80 Ah or less. The 15% deration is a conservative mid-life estimate — appropriate for batteries with 200–500 cycles, or batteries of unknown age. For new batteries, leave this unchecked. For batteries approaching end of life (typically defined as 80% of original capacity), you may want to apply a larger manual deration by simply reducing the capacity value you enter.