Parasitic Battery Drain: Symptoms and How to Detect It
Key Takeaway
Battery dead every morning? Something is draining it when the car is off. Here's how to find it.
Signs of Parasitic Drain
| Symptom | Indicates |
|---|---|
| Dead battery after sitting overnight | Active drain present |
| Dead after a weekend of not driving | Moderate drain |
| Slow cranking after sitting | Battery being partially drained |
| New battery dies within weeks | Drain is killing the battery |
| Clock/radio reset frequently | Battery dropping too low |
How to Find the Drain
1. Set multimeter to amps (10A or 20A DC scale).
2. Disconnect negative battery cable.
3. Connect multimeter in series between the cable and terminal.
4. Wait 30 minutes for modules to go to sleep.
5. Read the current. Normal: 20-50 mA. Problem: >75 mA.
6. Pull fuses one at a time. When the draw drops, you found the circuit.
Common Parasitic Drain Sources
| Source | Draw |
|---|---|
| Glove box light stuck on | 500+ mA |
| Trunk light stuck on | 500+ mA |
| Aftermarket radio/amp | 100-500 mA |
| Faulty door switch | 200+ mA |
| Dash cam without cutoff | 300+ mA |
| Failing BCM module | 100-300 mA |
ProHow Steer Helps
Steer monitors battery voltage while the car is parked. If voltage drops faster than expected, you'll get an alert indicating a possible parasitic drain.
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