Parasitic Draw Battery Drain Calculator

Estimate how long a key-off electrical draw will take to drain your battery.

Estimate Drain Time

Most vehicles should settle under 50 mA after sleep mode. A higher draw can drain a healthy battery in days.

How the Estimate Works

We convert the parasitic draw from milliamps to amps, then divide the usable battery capacity by that draw. The minimum state of charge represents the point where cranking can become weak.

  • Battery capacity: Typical passenger vehicles range from 45 to 80 Ah.
  • Minimum state of charge: Many no-starts happen around 50 to 70% depending on battery health and temperature.
  • Parasitic draw: Over 100 mA is usually excessive once the vehicle goes to sleep.

Tips for Accurate Draw Testing

  1. Let modules sleep: Some cars need 20 to 40 minutes after key-off to settle.
  2. Measure at the battery: Use a multimeter in series on the negative cable.
  3. Pull fuses one by one: A sudden drop identifies the circuit with the draw.