Battery Drain Test

WARNING: Do not attempt this test on a lead-acid battery that has recently been recharged.

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

NOTE: Many computers draw 10 mA or more continuously.

NOTE: Use an in-line ammeter between the battery positive or negative post and its respective cable.

NOTE: Do not start vehicle with clip on cable.

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See 1996 COMPUTER RELEARN PROCEDURES -- FORD MOTOR CO. in GENERAL INFORMATION before disconnecting battery.

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 the following procedure.

Voltmeter Drain Testing

Connect test leads in the input terminals shown. See Fig 1.Do NOT start vehicle with multimeter connected in line with battery cable and battery.
Turn switch to mA/A DC.
Disconnect battery terminal and touch probes as shown. See Fig 1.
Isolate circuit causing current drain by pulling out one fuse after another while reading the display.
Current reading will drop when the fuse on the bad circuit is pulled.
Reinstall fuse and test components (including connectors) of that circuit to find damaged component(s).

Typically, a drain of approximately one amp can be attributed to an engine compartment 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 test lamp will go out or 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.

The current reading (current drain) should be less than 0.05 amps. If it exceeds 0.05 amps it indicates a constant current drain which could cause a discharged battery. Possible sources of current drain are vehicle lamps (engine compartment lamp, glove compartment lamp, luggage compartment lamp, etc.) that do not shut off properly.

If the drain is not caused by a vehicle lamp, remove the fuses from the interior fuse junction panel, one at a time, until the cause of the drain is located. If drain is still undetermined, remove fuses one at a time at the main fuse junction panel to find the problem circuit.

Electronic Drains Which Shut Off When the Battery Cable Is Disconnected

Repeat steps 1 through 6 of the Voltmeter Drain Testing.
Without starting engine, turn ignition ON for a moment and then off. If applicable, wait one minute for the illuminated entry lamps to turn off.
Connect the voltmeter and read the voltage.

The current reading (current drain) should be less than 0.05 amps. If it exceeds 0.05 amps after a few minutes, and if this drain did not show in previous tests, the drain is most likely caused by a malfunctioning electronic component. As in previous tests, remove the fuses in interior fuse junction panel one at a time to locate the problem circuit.

Fig 1: Performing Battery Drain Test

Courtesy of FORD MOTOR CO.