Car Battery Draining Overnight in Chennai?
A battery that goes flat overnight has a specific cause — parasitic current draw, a failing battery, or an alternator that isn't recharging properly. GM diagnoses the actual fault before recommending a fix. Ambattur workshop, Mon-Sat 10AM-8PM.
Quick answer: A car battery draining overnight is caused by parasitic current draw (a component staying on after ignition-off), a battery that can no longer hold charge, or an alternator not charging properly. Each needs a different diagnosis. Call +91 8428000085 to book at GM's Ambattur workshop.
Three Reasons a Battery Drains Overnight
1. Parasitic Current Draw
A component stays on after the ignition is off — a relay, blower motor, interior light, alarm module or after-market accessory. Even 200mA of draw empties a battery in 8-12 hours. Most common cause.
2. Weak or Failed Battery
Chennai heat degrades car batteries faster — typical life is 2-3 years. An old or heat-damaged battery loses capacity and can't retain charge overnight even without a parasitic fault. Confirmed by load test.
3. Alternator Not Charging
If the alternator output is below 13.5V, the battery slowly discharges while driving and goes flat after parking. Checked with a voltmeter under load.
GM's Battery Drain Diagnosis Process
We don't replace parts until we know what's wrong.
Battery Load Test
The battery is tested at its rated CCA. A battery that fails this test needs replacement regardless of other findings. If it passes, the drain is coming from somewhere else.
Alternator Output Check
With the engine running and electrical loads on (AC blower, lights), the alternator should read 13.5-14.5V. Below this means the battery is not being recharged properly.
Parasitic Draw Test
A current clamp is placed on the negative battery terminal with ignition off. After 10-20 minutes (for all modules to sleep), draw is measured. If above 50-80mA, fuses are pulled circuit by circuit to locate the faulty system.
Confirm & Fix
Once the fault circuit is isolated, the specific component is identified and the repair is recommended — relay replacement, wiring repair, or battery/alternator replacement. Estimate confirmed before work begins.
Battery Drain — Questions Answered
Battery Draining Overnight?
Call or WhatsApp GM Car A/C Service, Ambattur. We diagnose the actual cause before recommending a fix — no guesswork replacements.