Quote:
Originally Posted by zajo
The brand new battery that was happily cranking the engine two days ago is *completely* drained! In two days!
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You need to do some simple tests that require a Digital Multi Meter (DMM) with a DC current capability of 10A. They're available for under $50.
To find out if anything is draining the battery...
Set the DMM to DCA 10A.
Disconnect the negative terminal of the battery and insert the DMM leads in series with the negative ground cable and the negative post of the battery.
You should see all zeros. If so, set the DMM to DCA 200 mA. You should see maybe 20 mA; not much more (make sure all your interior and hood compartment lights are OFF).
If you see larger numbers such as 100 mA for example, you then start removing fuses one at a time till you see the reading go to near zero. That fuse is the circuit that is drawing current.
Once you start the car...
Set the DMM to DCV 20V.
Measure the voltage across the battery with teh engine running and the headlights on and the engine reving at about 2000 RPM. You should see your voltage at about the low 13V up to 14.4V maximum...or at least increasing if the voltage is lower.
Thats why installing a voltmeter in the car is such a good idea. It tells you what your charging system is doing. An ammeter is far less useful.