CASE 001
Battery Discharges Overnight
intermediate
20 min
Petrol
Vehicle
- ModelTraining Compact 1.4
- Engine1.4 MPI
- Mileage94,000 km
Customer complaint
The engine cranks slowly in the morning. The customer reports the battery has been replaced twice and the problem returns within a week.
History
New battery fitted 8 days ago, then again 2 months ago. No warning lights. Alternator was replaced 6 months ago (per invoice).
Live data
- Battery voltage, engine off (rested)12.2 V
- Charging voltage, idle14.1 V
- Charging voltage, loaded13.9 V
Measurements
- Parasitic drain, all modules asleep620 mA
- Battery conductance testPasses
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Diagnostic case
Next step — Reasoning.
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Confirmed cause
Excessive parasitic current draw while the vehicle is asleep (a module not going to sleep).
Reasoning
The battery itself passes and the charging system is healthy, so the energy is being consumed while parked. A healthy vehicle typically settles to a very small drain — often tens of milliamps, and the exact limit is manufacturer specific. At around 620 mA the battery is empty within a couple of days.
Recommended repair
- Identify the module that fails to sleep using current measurement and fuse/relay isolation.
- Repair or replace the offending module or its wiring.
- Re-measure the drain after the repair and confirm the battery stays charged.
Related tools
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.