GARAGE WORKSPACE / 01

Parasitic draw:
find where charge goes.

Turn sleeping-current readings into a clearer next check. Model battery reserve, compare measured circuit drops, and keep your progress.

Open the parasitic draw calculator ↓

01 Vehicle & battery02 Isolate & measure03 Read the result

Enable JavaScript to use this calculator. You can still read the parasitic draw testing guide.

01 / BASELINE

Your starting point

Vehicle year Make Model

Vehicle details label your session. Use your manual for actual fuse locations and limits.

Battery type Rated capacity (Ah) Starting charge (%) Chosen reserve (%)

Sleeping current 250 mA Service-manual draw limit (mA)

50 mA is a starting comparison value, not a universal specification. Battery type does not apply an invented capacity multiplier.

02 / CIRCUIT WORKSPACE

Follow the current drop

Enter the current reduction you measured for each circuit. Select isolated circuits to model the remaining draw. These are circuit groups, not a fuse-position diagram.

Interior

Radio / infotainmentInclude isolated circuit Measured drop (mA)

Body control / lightingInclude isolated circuit Measured drop (mA)

Accessory / dash cameraInclude isolated circuit Measured drop (mA)

Under-hood

Engine control supplyInclude isolated circuit Measured drop (mA)

Relay / auxiliary supplyInclude isolated circuit Measured drop (mA)

Other measured circuitInclude isolated circuit Measured drop (mA)

Removing a fuse can wake modules. Repeat the sleep procedure. Drops measured separately may overlap and cannot prove which component failed.

03 / MODELLED RESULT

What your readings suggest

Remaining sleeping draw250 mA250 mA

Time to 50% reserve120.0 hours · 5.0 daysConstant-current estimate; not a guaranteed starting window.

Circuits to investigate

Record a measured drop to identify a circuit to investigate.

Remaining draw exceeds your entered service limit.

Inputs stay in this browser when device storage is available.

Understand the estimate

Hours = rated amp-hours × (starting charge − chosen reserve) ÷ 100 ÷ remaining amps. A 60 Ah battery starting at 100%, with a 50% reserve and a 250 mA draw, reaches that reserve in about 120 hours.

Actual no-start time depends on battery health, temperature, self-discharge, engine cranking requirements, and intermittent loads. A current drop identifies a circuit to investigate; it does not diagnose a failed BCM, radio, or alternator.

Compare your readings with the sleeping-current guide, follow the fuse isolation procedure, or investigate battery and alternator symptoms.

Use the right measurement

The input is milliamps, abbreviated mA. Divide milliamps by 1,000 to get amps: 250 mA is 0.25 A. Use the battery's rated amp-hour capacity; cold-cranking amps describe a different property and cannot be substituted. Your chosen reserve is a modelling assumption rather than a universal starting threshold.

Record a baseline only after the vehicle has completed its manufacturer-specified sleep procedure. Opening a door, unlocking the vehicle or disconnecting a circuit may change that state. Use an appropriate current clamp or the exact meter procedure for your vehicle and equipment. Fluke's parasitic draw testing guidance and Pico's clamp-method procedure explain why instrument setup and sleep state matter.

CONTINUE FROM YOUR SYMPTOM

Choose the next check before buying parts

It will not start now

Use the dead-battery recovery guide before a draw test. Resolve immediate safety and power needs first.

It keeps losing charge

Compare repeated battery failures with your charging and parking pattern. A draw calculation cannot test battery health.

You have a sleeping-current reading

Use draw-testing and circuit isolation guides to compare measurements safely and repeat them under the same conditions.

A warning or accessory is involved

Look through vehicle systems and accessory checks, or use the complete guide library when the cause remains unclear.