Drain Testing Procedures

WARNING: DO NOT ATTEMPT THIS TEST ON A LEAD-ACID BATTERY THAT HAS RECENTLY BEEN RECHARGED. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY.


CAUTION: Do not crank the engine or operate accessories that draw more than 10 A. As this could blow the fuse in the meter.


NOTE:
- Many computers draw 10 mA or more continuously.
- Use an in-line ammeter between the battery negative terminal and its respective cable.

Check for current drains on the battery in excess of 50 milliamps with all the electrical accessories off and the vehicle at rest. Current drains can be tested with this procedure.
1. Disconnect battery ground cable.
2. Connect black lead on ammeter to ground (-) post on battery.
3. Connect red lead on ammeter to battery ground cable.
4. Isolate circuit causing current drain by pulling out one fuse at a time while reading the display.
5. Current reading will drop when the fuse on the relevant circuit is pulled.
6. Reinstall the fuse and test components (including connectors) in that circuit to find damaged component(s).

Typically, a drain of approximately one amp can be attributed to interior lamp, glove compartment lamp, or luggage compartment lamp staying on continually. Other component failures or wiring shorts may be located by selectively pulling fuses or disconnecting fuse links to pinpoint the location of the current drain. When the current drain is found, the meter reading will fall to an acceptable level. If the short is still not located, after checking all the fuses and fuse links, the drain may be due to the generator.

Test Conclusion
The current reading (current drain) should be less than 0.05 amp. If it exceeds 0.05 amp, it indicates a constant current drain which could cause a discharged battery.