Battery Life Calculator

Instantly estimate how long your device will run on a single charge — or find out what battery capacity you need for a target runtime. Works for smartphones, laptops, tablets, IoT sensors, drones, and more.

Device Presets

<h3>Battery Capacity</h3>
<div class="field-row">
  <div>
    <label>Capacity (mAh)</label>
    <input type="number" id="bl-mah" value="4000" min="1" step="100">
  </div>
  <div>
    <label>Battery Voltage (V)</label>
    <input type="number" id="bl-voltage" value="3.7" min="0.1" step="0.1">
  </div>
</div>

<h3>Power Consumption</h3>
<div class="power-toggle">
  <label><input type="radio" name="bl-power-mode" value="ma" checked onchange="blTogglePowerMode()"> Current draw (mA)</label>
  <label><input type="radio" name="bl-power-mode" value="w" onchange="blTogglePowerMode()"> Wattage (W)</label>
</div>
<div class="field-row">
  <div id="bl-ma-field">
    <label>Current Draw (mA)</label>
    <input type="number" id="bl-ma" value="150" min="0.1" step="10">
  </div>
  <div id="bl-w-field" style="display:none;">
    <label>Power (W)</label>
    <input type="number" id="bl-w" value="0.555" min="0.001" step="0.1">
  </div>
  <div></div>
</div>

<div class="slider-row">
  <label>Efficiency Factor: <strong id="bl-eff-label">85%</strong> <span class="badge">Real-world loss</span></label>
  <input type="range" id="bl-efficiency" min="70" max="95" value="85" step="1" oninput="document.getElementById('bl-eff-label').textContent=this.value+'%'">
  <div class="slider-labels"><span>70% (Poor)</span><span>80%</span><span>90%</span><span>95% (Ideal)</span></div>
</div>

<button class="calc-btn" onclick="blCalculateRuntime()">Calculate Runtime</button>

Battery Energy

Effective Power Draw

Efficiency Applied

Runtime (decimal)

Tips for Extending Battery Life

Avoid full discharges. Lithium batteries last longer when kept between 20–80% charge. Deep cycling accelerates capacity loss.
Reduce screen brightness. The display is the single largest power consumer in most mobile devices — cutting brightness 30% can extend runtime 15–20%.
Disable background refresh. Apps syncing in the background can consume 10–25% of battery without you noticing. Enable it only for critical apps.
Mind the temperature. Batteries discharge faster in cold and degrade faster in heat. Ideal operating range is 15–25°C (59–77°F).
Use low-power or airplane mode. Radio transmitters (Wi-Fi, LTE, Bluetooth) are heavy consumers. Disable unused radios for a significant runtime boost.
Slow-charge when possible. Fast charging generates heat, which degrades battery cells over time. Overnight slow-charging extends overall battery lifespan.
Match charger to device. Using an underpowered or overpowered charger reduces efficiency and can stress cells. Always use the manufacturer-recommended output.
Store at 50% for long-term. If storing a device unused for weeks or months, keep it at around 50% charge in a cool, dry place.

How Battery Life Is Calculated

The core formula is straightforward:

Runtime (hours) = (Capacity in mAh × Efficiency) ÷ Current Draw (mA)

Or, using watt-hours:

Runtime (hours) = (Capacity in mAh × Voltage × Efficiency) ÷ Power (W) ÷ 1000

The efficiency factor accounts for real-world losses: heat generation in battery cells, voltage conversion losses in the device's power management IC, and the fact that batteries cannot fully discharge to rated capacity under load. A value of 85% is a good general estimate for lithium-ion cells; older or colder batteries may warrant 70–75%.

Battery Life Calculator - Estimate Device Runtime