Battery voltage and dc dc charger

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Hi Terry,

Possibly because your meter calibration is reading high. And I am not being facetious.
What sort of meter is it?
What does it read at the beginning of the night?
What does it read with no input voltage?

In my experience, many meters are described as having better accuracy than they actually deliver. Rather like tyre pressure gauges.

G'day,

as Allan pointed out, meter accuracy should be checked first.
Multimeters usually are of sufficient accuracy, but small digital voltmeters including plug in types and hard wired can easily be out by 0.2V.

The other thing, Chinese made AGM batteries often have resting voltages of 13.1V to 13.2V when fully charged.
Looking at the combined 360Ah?, a few Ah of discharge overnight won't bring the SOC down sufficiently for a more noticeable drop in the resting voltage.

#1 and above all, as has been mentioned previoulsy, you need to be sure of the accuracy of your voltmeter.

In this day and age, very high accuracy can come realy cheap, but that does not mean ever meter is accurate or will stay accurate.

Because I am in the electronics business, I have several meters I can compare to get a reasonable impression of accuracy.

Most digital meters I encounter are spot on ... well at least to 1 decimal point., BUT I do occasionally encounter meters that are one or two decimal points off on a 15 volt scale.

It is so very important that you meter is accurate or you at least know what the error is when dealing with batteries where one whole volt can mean the difference between a battery being pretty damn fine and dead as a maggot.

#2 Some batteries take quite some time to return to what could be considered their real resting voltage ...... this is good it is an indicator of battery health and quality ...... a battery that takes a long time to reach its real resting voltage will have low self discharge .. this is a good thing.

If you are getting pedantic and want to know the real resting voltage of a battery, charge it well, disconnect it from everything and leave it 24 hours before calling it "rested".

Some batteries will remain at a higher voltage and at an above normal resting state of charge for days or weeks.

#3 the generic state of charge voltages are fine and beaut and do work reasonably well for everyday batteries.

BUT if you want realy meaningfull figures you need to get state of charge graphs for that specific battery AND there will be multiple temperature corrected curves.

Even then, voltage is only a sign of state of charge not a hard and fast actual measure .... the only truly reliable measure of state of charge is specific gravity of the electrolite which we simply can't measure in sealed batteries.

#4 an important thing to understand is that a single voltage reading gives us only a fleeting glimpse of what is going on .... if we want to know what realy goes on with a battery, we need to take multiple readings over time and thru state of charge

It must be understood that battery behaviour is far from linear and far less consistent than many would like to believe.

There are so many factors that influence battery behaviour ...... anybody that things they have a realy accurate measure of what is happening with the battery is dreaming.

cheers

hi
agm typically have a fully charged volts of 13.0 or greater
flooded/wet typically have fully charged volts 12.7 or greater

If u can get volt chart from the batt maker would be ideal.

Although batt volts are used even by battery chargers .
Measuring amp in/out is the most accurate .