Battery Life / Runtime Calculator
指导
Battery Life / Runtime Calculator
Estimate how long a battery will power a device from its capacity, voltage and load. The calculator handles mAh, Ah and Wh inputs, series/parallel cell arrangements, depth-of-discharge limits, system efficiency and the Peukert exponent for lead-acid chemistries. Output includes pack totals and time remaining at 100%, 80%, 50% and 20% state of charge.
如何使用
- Pick the unit for your battery capacity (mAh, Ah or Wh) and enter the rated value from the datasheet.
- For mAh or Ah, enter the nominal cell voltage and how many cells are wired in series and parallel. For Wh, enter the pack’s nominal voltage.
- Enter the load — either current (mA / A) or power (W) — drawn by the device.
- Adjust the depth of discharge, system efficiency and Peukert exponent sliders to match your chemistry and use case.
- Read the pack summary, total runtime and the time remaining at lower states of charge.
特征
- Three capacity units – Switch between milliamp-hours, amp-hours and watt-hours.
- Three load units – Enter device draw in milliamps, amps or watts.
- Series and parallel cells – Calculate pack voltage and total capacity from individual cell specs.
- Depth of discharge slider – Reflect the safe usable range for your chemistry.
- System efficiency slider – Account for converter, inverter and wiring losses.
- Peukert exponent – Apply a lead-acid correction factor (1.0 = ideal, ~1.2 = typical lead-acid).
- State-of-charge breakdown – See remaining runtime at 100%, 80%, 50% and 20%.
- Auto-updating results – All outputs recalculate as you change inputs, with no Generate button.
常见用例
- IoT and embedded – Size LiPo or coin cells for sensors with sleep current and short bursts.
- Solar and off-grid – Size lead-acid or LiFePO4 packs and apply Peukert correction.
- Drones and RC – Cross-check spec sheets against measured wattage in flight.
- UPS and backup power – Estimate how long a UPS will keep a server alive at a given load.
- Power tools and e-bikes – Compare 18650 packs of different S/P arrangements.
常问问题
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What is Peukert's law and when does it matter?
Peukert's law describes how the usable capacity of a battery drops as the discharge current increases. The relationship uses an exponent k: a battery rated 100 Ah at a 20-hour discharge may only deliver 70–80 Ah when drained in one hour. The effect is dominant for flooded and AGM lead-acid (k ≈ 1.1–1.3) and negligible for lithium-ion or LiFePO4 chemistries, where k is effectively 1.0.
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What is depth of discharge (DoD) and why does it shorten runtime?
DoD is the percentage of the rated capacity you allow to drain before recharging. Most chemistries cannot be discharged to 0% safely — lithium-ion BMSs usually cut off at 10–20% to protect the cells, and lead-acid is typically limited to 50% to extend cycle life. Multiplying the rated capacity by DoD gives the realistic energy you can pull from the pack on each cycle.
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How does series versus parallel cell configuration change the pack?
Series connections add voltages while keeping the amp-hour capacity of a single cell. Parallel connections add amp-hour capacity while keeping voltage constant. A 4S2P pack of 3.7 V / 2,500 mAh cells produces 14.8 V at 5,000 mAh (74 Wh total). Total energy in watt-hours is the same regardless of arrangement, but the voltage and current characteristics differ significantly.
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Why does converter efficiency belong in the calculation?
Battery energy is rarely consumed at the pack voltage. DC-DC converters, linear regulators, and inverters all dissipate part of the energy as heat. A 90% efficient buck converter delivers only 0.9 watts to the load for every watt drawn from the battery; an off-grid sine wave inverter is often 80–85% efficient. Multiplying usable capacity by this efficiency factor gives a realistic runtime estimate.
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What is the C-rate and how does it relate to runtime?
The C-rate expresses discharge current as a multiple of the pack's rated capacity. A 10 Ah pack discharged at 1C draws 10 A and empties in roughly one hour; at 0.5C (5 A) it lasts two hours. Datasheets usually specify capacity at a particular C-rate (often 0.2C or 0.05C). Discharging at a much higher C-rate than the rated test triggers the Peukert effect and reduces deliverable capacity.
