beerismygas wrote:
i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx

The output waveform from the charger is a rectified sine wave. It will
not read correctly on a dc meter. If it is a half wave rectifier, it
will not read correctly on the ac scale either. If you want to see what
it is doing, look at it on a scope. You can charge a 12v battery with
a waveform that reads nearly zero on a voltmeter because of the peak
to average ratio of a waveform.

If the meter reads a real current going into a 12V battery, it is still
charging.