Battery volt numbers

[davidpm]

The books say a full batter should be 22.6 Volts
I've got one that reads 13.06 and one that reads 12.87

There is no float charge, they were sitting for a day.

Is this normal or do I need a new meter?

[Maine Sail]

Flooded, GEL, AGM? What brand and what does the manufacturer call full? Most batts are full at around 12.7 +/- but each manufactuerer is slightly different. Trojan flooded batts are 12.72 full. Some AGM batts will hold a surface charge for quite a while where wets are usually ready for OCV readings at 12-24 hours rest. Throw a load on them and see if it wipes the surface charge then re-test. DVM's are usually out by the hundreths not the tenths, unless you have an analog meter, and then all bets are off.

[MARC2012]

12.6?marc

[davidpm]

They are flooded. Next time I get to the boat I'll check the brands. They are different brands.
After further research the 12.8 is considered in range.
Was a little surprised by the 13 though.

[billyruffn]

Most battery chargers push wet cell batteries to 14.4 during the bulk charge phase, and then reduce the charge to 13.7 or so for the absorption phase for a set period of time, and then move on to the trickle phase where they hold the battery at 13 or so volts. With the charger turned off the batteries will hold a charge above 12.7 or 12.8 for a period of time. If you arrive at the boat and find the batteries at 12.7 or 12.8 or slightly higher, don’t worry, mon! Be happy! It means they’re in good shape.

[hellosailor]

" 22.6 Volts"
David, I expect that's a typo for 12.6?

Only the battery maker knows the exact number for their battery chemistry, they all vary a bit. 13+ means there is either a float charge still on the battery, or a bad meter. 12.8 would be surprisingly high for a brand new battery no matter who made it.

If you really want to trust your meter, you do need to use a calibrated meter. Either lab calibrated, or bought new and calibrated when made (i.e. a pricey Fluke) or you need to find a way to calibrate it, something to compare it to. And then you need to find out the limits of your meter.

Some may be rated accurate to 1/2% on the 20VDC scale, others to 1-2% plus or minus 3 righthand digits. So at a real 12.6 volts...You may see 12.4 on a meter that's only one percent off, 12.1 or 12.9 on a meter that's got more float in it.

I've got a spare disposable Harbor Freight meter, it's almost as accurate as a Magic8Ball. I keep meaning to pick up a Fluke, because my better meter still isn't in that class. But it isn't easy to find a "12" volt calibration source!

[davidpm]

Back to the boat, same meter:
Switch set to off
Bat #1 12.98
Bat #2 12.83
Switch set to #1 9.9 mercury running about half throttle
Bat #1 14.6
Bat #2 12.83

So it looks to me like the batteries and meter are both in range.
But maybe my meter reads a little high.

[btrayfors]

Not necessarily. Batteries differ in their chemistries and their resting voltages.

In any case, voltage measurements don't mean much unless the batteries have been resting (no load and no charge) at least overnight.

Re: multimeter accuracy, you might try your meter against these voltages. The 9V is best, because it's closer to 12V which is normally what's measured on boats.

ALL ARE AVERAGE MEASUREMENTS TAKEN FROM FRESH DURACELL ALKALINE BATTERIES BY A FLUKE 189 METER:

Size AA: 1.627V

Size C: 1.595V

Size D: 1.609V

Size 9V: 9.662V

Bill