Airportable wrote: It’s not as much the voltage that requires monitoring, it’s the current.
There is a shut down sequence which resets all circuits down to a quiescent current of around 250ma (this was the value on my car a couple of days ago). Even inexpensive digital multimeter have a 10amp range, once this range is selected, it can be introduced in series with the battery & a useful indication of the current being drawn indicated.
Don’t try & start the car with this connected, it will melt in a most impressive fashion.
M

I have a simple in line ammeter that plugs into the fuse holder, this allows you to see the current leakage through individual circuits. Actually I have 2 one is 20 amps and the other is 60amps.
You do need to make sure everything on that circuit is turned off, then you use it to replace the fuse and you can see how much current draw is through that circuit. if every thing is off then the reading will indicate not only a leakage but also it's magnitude.



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