Parasitic Battery Drain

Parasitic battery drain (also called parasitic draw) happens when something in the vehicle continues to use electricity from the battery after the ignition is turned off. While a small amount of draw is normal—like for the clock, security system, or ECU memory—excessive drain will slowly kill the battery, especially overnight or over a few days of non-use.

Common Causes of Parasitic Drain:

• Faulty relays (like a stuck fuel pump relay)

• Aftermarket accessories (improperly installed stereos, alarms, remote start, etc.)

• Glove box, trunk, or dome lights staying on

• Control modules not going to sleep (e.g., BCM or infotainment)

• Corroded or dirty battery terminals

• Shorts or wiring issues

Symptoms:

• Battery dies overnight or after sitting for a day or two

• Repeated need to jump-start the vehicle

• Dimming interior lights or flickering electronics

Conclusion:

Parasitic battery drain occurs when an electrical component keeps drawing power after the vehicle is turned off, leading to a dead battery over time. While a small draw is normal, excessive drain signals a problem—often caused by faulty wiring, stuck relays, or aftermarket accessories.

• Diagnosing it involves measuring current draw with a multimeter and isolating the faulty circuit by pulling fuses. Identifying and fixing the source prevents repeated battery failures and ensures reliable vehicle operation.