How to test 12V automotive battery charger?
 

I have an old Exide automatic battery charger that I'm not sure is charging properly. It's one of those that you just plug in and leave it. Has 2 slider switches.

Switch on left is for battery type and has 2 settings: 1-Deep cycle/maintenance free or 2- Regular/Gel

Switch on right is for charge type and has 4 settings: 1-6V 10amp, 2-12V 2amp, 3- 12V 10amp and 4- 12V 60amp engine start

On the left is a needle type guage that points to 3 batteries: Empty, half full and full.

I'd like to know the method for testing this thing with a voltmeter and what readings to expect.
Are readings taken while attached to a battery?

Thanks in advance, Craig

put the voltmeter on a battery and see what it reads. than hook up the charger and see if it is higher.