How to test battery draw with digital multimeter for both cases when engine is on & when engine is off ? thank?

How to test battery draw (car battery) with digital multimeter for both cases when engine is on %26amp; when engine is off (whether its off for 10 to 12 hours or its off for about a minute) ?





what should be the readings of a good battery %26amp; of a bad one ?





thankHow to test battery draw with digital multimeter for both cases when engine is on %26amp; when engine is off ? thank?
You can check current draw on a battery by turning off all accessories, lights, the ignition switch off, etc.





I have measured several vehicles when troubleshooting dying batteries.





Reasonable current draw for a modern vehicle would be somewhere near 250mA, perhaps a little bit more. I have seen 100ma or so more often.





There are a number of circuits (clock, stereo, etc.) that require a memory back-up, which is where the draw comes from (unless a fault is present).How to test battery draw with digital multimeter for both cases when engine is on %26amp; when engine is off ? thank?
The only thing you should be checking is the DC Voltage. If you try and test current by putting the multimeter in series you are at a minimum going to blow the multimeter fuse if not damage the meter.





Each battery should tell you the proper voltage. Your owners manual should also give you the proper range. My Jeep is somewhere between 12-14.4VDC. As a battery is discharged the voltage drops. Once the vehicle has started the alternator should produce the proper voltage (say 14.4VDC) for vehicle operation. If the battery voltage (while it is open circuted) is less than the alternator output voltage, current will flow from the alternator to the battery to recharge it. Eventually the two will be equal. When you turn the vehicle off (and thus turn the alternator off) if the voltage drops significantly there may be a problem with the battery. If you take it to any AutoZone or AdvanceAuto or similar store, they should be able to test your battery for free.





To take the measurements, switch the meter to VDC and range it to above 15or20v if it is not autoranging. place the black lead on the negative terminal and the red lead on the positive terminal. When the vehicle is completely off you can get your ';no load'; voltage. Start the vehicle and check it again. This is the ';running'; voltage. If there is constantly a large difference between the two you may have a problem. Each battery is slightly different but a typical vehicle is 12-14 volts normally.
You can measure the current indirectly, if your meter goes down to really low voltages, by measuring the voltage drop across the earth braid between the battery terminal and the chassis. You can calibrate this ';ammeter shunt'; by turning on the headlights; assuming they are rated 60W each, this will add another 120 watts == 10 amps to the current consumption.