Battery Parasitic Drain Test
If a known good battery continues to die overnight or in a short period, suspect a parasitic drain. The drain could be caused by a short in the system, a small light, or an accessory drawing current overnight.
Connect a multimeter in series between the negative battery terminal and the negative battery post; current is measured as it flows through the meter. If the measurement is above 50mA, identify the circuit causing the drain by locating and removing each fuse until the reading on the meter drops to or below specifications.
Most likely, something like a light or an accessory was left on, but sometimes it’s the component, wire, or its connector. A circuit diagram may be necessary to identify and trace the circuit. Once found and repaired, measure the battery drain again to ensure it’s within specifications. Check with the manufacturer for specifications and any special procedures.