Battery "Full Charge" or Not?

[D Davis]

The more I read the more confused I am about a "FULL CHARGE" on a battery. I have a 24 group AGM Battery. A 3 stage Progressive Dymanics
Power converter/charger and a Volt Minder to read the Battery charge.
What I have read says that a FULL CHARGE on a 12 volt battery should be
between 14.4 V and 14.8 V. My converter, which is new only charges to 13.5V. Sometimes I get 13.7 or 13.9 V. after charging for 24 hours then taking a reading 3 hours after that.
So my question is, am I running around with an unfully charged
battery? What do most people do about this? Cart a Large battery charger with them? Really? And do not have Solar Panels...
Any thoughts would be appreciated.

[Robert Detrick]

a fully charged 12 volt battery will read 12.6 volts. when first removed from a charger may show close to 14 volts,then slowly drop off but should eventually be stable at 12.6 volts. I use a battery doc. maintainer on my battery at home.

[D Davis]

Originally Posted by Robert Detrick

a fully charged 12 volt battery will read 12.6 volts. when first removed from a charger may show close to 14 volts,then slowly drop off but should eventually be stable at 12.6 volts. I use a battery doc. maintainer on my battery at home.

Robert, what is a doc. maintainer? I have read to recharge as soon as you get home. Which is what I do. Thank you for your response.

[gmw photos]

14.4 or more ( up to maybe a peak of around 15V ) would be considered a charging voltage. In other words if you put your voltminder in your tow vehicle, and drive down the road, you would typically see around 14.1 to 14.3 normally.

A 'fully charged' 12V battery usually reads around 12.6 or with no load. From the numbers you posted, it looks like your system is working correctly.

Go camping. Have fun. Don't fret over it.

[gmw photos]

Another similar to the battery doc that Robert talks about is "battery tender". That's a brand name.

I should have added this in my above comment: Usually, I just plug my camper in to shore power when I get home, and let the battery charger in the camper ( part of the 'converter' ) maintain the battery. Also, if you have a rather lengthy drive home, your alternator in your tow vehicle is charging the trailer battery too ( if you are using a standard 7 pin RV connector between the trailer and tow vehicle ). Although the charging from the TV to the trailer is "rather slow".

[D Davis]

Thank you George.

[Robert Detrick]

a battery tender is a low current or amperage battery charger that you can leave attached to your battery between trips. Because of the low current it will not boil your battery. When i am dry camping i use an 80 watt. solar panel with a charge controller to regulate charging. If noise is no a problem you can get a small quiet generator.

[gmw photos]

You're welcome.

It's honestly a little misleading and somewhat inaccurate to take a voltage reading of a battery with 'no load' on it. In other words, it can show 'good' but then when you actually apply a load to it, it may drop too much, and not actually be good. That's why when you go to the shop ( car dealer or big auto parts house ) they have a battery tester they connect to it that applies a predetermined load to the battery, and watches the voltage as the load is pulling on the battery. The 'good' testers like that, you might see in car dealer shop, even spits out a printed paper 'report' on the condition of the battery. That's really the correct way to test a battery.

You didn't say how old your battery is. But that too can be misleading. I've seen them fail in a year or so....and I've seen them last for 7 or 8 years. Almost seems to be the luck of the draw.

I tend to approach it this way: if a part is 'mission critical', then you should replace it on fairly short cycles. On the other hand, if it's something you can live without for a few days while on the road, then just keep running it, and replace it if you have to while you're out.

[D Davis]

Thanks Guys.

[gmw photos]

And to take what Robert said one step further regarding battery tender and battery doc type chargers, they are so called "smart" chargers. They "look" at the battery, determine what the battery needs, and apply the correct voltage and current, continue to monitor the battery during the charge cycle, then taper off, and eventually go into a mode of just 'watching' the battery. Then as it drops in potential, just from sitting, the charger comes back on and again applies the correct power to the battery.

I use them on my motorcycle batteries and even on my portable photography studio strobe power supply battery. Smart chargers are really nice.