On Step #4, (Disconnecting the ground cable & connecting a Amp meter between the battery post & the ground cable, is this test done with the Engine Running OR OFF? Thanks in advance for any help!!!! Richard

1 Answer 1


A normal multimeter can measure max 10-20A, and this also for short time only. This current is easily exceeded when the motor is running, or when it's not running and heavy consumers such as headlight or rear window heater are running. This can destroy your multimeter!

When staring the motor, it can draw several 100A from the battery, this will definitely kill a normal multimeter, it might even catch fire. And it is possible that disconnecting a battery when the motor is running can destroy something in the car, too.

Since you want to check if the car drains the battery, switch off everything. Also close the doors, even the bonet, and lock the car. Otherwise, the electronics might not go to sleep, and draw more current than it would normally. And since it takes some time until the car sleeps, observe the current for a minute or so.

With the motor running (and may be revving a little), the battery voltage is measured. It should be higher than with motor off and be in the order of 14V. This indicates that the battery is charged.

  • Well, you can put an ammeter / multimeter in series with the battery if you know what you are doing... And I have done it many times to find out what the alternator was up to. Don't try putting starter current through it... You have to make the connections once the engine is running - without breaking contact otherwise the alternator can be destroyed.
    – Solar Mike
    Jan 26, 2019 at 13:33

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