should a car battery charger read 12.0v?or more?

Without a load on it, a 12V charger will normally read 16-18V, when you connect it to a battery the voltage will drop down to whatever the battery wants it to be at.

How old is the charger ? In the good ol' days, there was no electronics in a car battery charger - just a pretty inefficient rectifier glued on the end of a power transformer. This produced a very 'pulsy' output, which if you read with a digital multimeter, may very well give a reading of less than you are expecting A fully charged battery is likely to read over 13V. Your car charges it at 13.8V nominal. Most '12V-rated' equipment for use in cars, is *actually* specced at 13.8V. The accepted output voltage range of a stand-alone charger is about 14 to 15V.If the meter on the front shows *any* forward current flow at all, then the output of the charger *must* be above the terminal voltage of the battery that it's connected to, at least *some* of the time - ie at the peaks of the output wave, if it is an old tranny plus reccy design. It's basic physics really.

Arfa

That's incorrect. The accepted figure for a discharged battery is 10.8 volts. Could also be zero, of course. ;-)

If the charger has some form of electronic regulation the open circuit voltage could be anything - as it may not 'switch on' properly until it sees a load. But if it did produce 12 volts it will partially charge a flat battery, but not fully. However, you should measure the voltage it produces while charging. Something near 14 is needed to charge a battery that is near fully charged - the voltage will likely be lower if the battery is near flat.

Nominally 14-15 VDC.

I doubt any domestic charger could give 15 volts across a good battery, nor is it desirable.

However, you should measure the voltage it

i tried it while charging and read 14v this time. 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.

Chargers today have lots of features that may make measuring the charger output voltage pointless. Even the simplest chargers use an unfiltered, unregulated voltage source. When you convert from RMS voltage to peak voltage you gain 1.4142 times the RMS voltage - the battery only sees and charges on the peaks of the rectified sine wave.

To check mine I use a large capacitor and charge it to 9 volts then place that across the charger terminals - then read the voltage. 14.9 volts most days.