Battery Parasitic Drain Test

If a known good battery continues to die overnight or in a short period of time, suspect a parasitic drain. This is current above an acceptable range of 50mA. The drain could be caused by a short in the system or a small light or an accessory may have been accidentally left on overnight.

By connecting a multimeter in series between the negative battery terminal and the negative battery post, current can be measured as it flows through the system. If the measurement is above 50mA, the circuit causing the drain can be identified by locating and removing each fuse until the fuse that protects the faulty circuit is found. This circuit will be noticed as a drop in current on the display. A legend will typically identify the demanding circuit.

Check each fuse until the faulty circuit is found.

Most likely something like a light or an accessory has been left on, but sometimes it’s the component, wire, or its connector that’s been damaged. This is when a circuit diagram can become necessary to identify and trace the circuit. Once found and repaired, measure battery drain again to insure it’s within specifications. Check with the manufacturer for any special procedures and specifications.