Battery Life Calculator (mAh to Hours)

Estimates how long a battery will power a device by dividing the battery capacity (in mAh or Ah) by the device's current draw, adjusted for efficiency losses. Worked example: a 3000 mAh phone battery powering a 150 mA load lasts 3000/150 = 20 h ideal; at 90 percent efficiency expect about 18 h before the 3.2 V cutoff. Halving the load current doubles runtime but not exactly twice in lead-acid: at very light discharge the Peukert effect works in your favor, often returning 105-110 percent of the rated amp-hours.

1. 1

   Step 1

   Enter the battery capacity (mAh or Ah)

2. 2

   Step 2

   Enter the device's current consumption

3. 3

   Step 3

   Adjust efficiency percentage (accounts for losses)

4. 4

   Step 4

   View estimated runtime in hours, days, or weeks

• 1

  Typical efficiency is 80-90% for DC-DC converters

• 2

  Peukert effect reduces capacity at high discharge rates

• 3

  Li-ion batteries: multiply Ah by 3.7V for Wh capacity

• 4

  Consider 20% capacity degradation for aged batteries

• Ignoring efficiency losses in voltage conversion

• Not accounting for the Peukert effect at high currents

• Using rated capacity without temperature derating

• Forgetting sleep mode vs. active mode current differences