Fully charged 12 volt battery

Hi Ian,

..Is the battery fully charged at around 12.8v but requires over 13.8v to get there?.

Yes, that's correct. The lower voltage is measured in open circuit (no battery current), and the 13.8V when charging current flows through the battery.
The 14.5V is a necessity too, to counter any sulphation which otherwise could form. But the 14.5V have to be time limited to 1~2 hours per day.
You can skip the 14.5V stage if the state of charge wasn't allowed to drop much below 80% in the previous night.
At every 14.5V charging session, the batteries lose a little bit of electrolyte, but that's only a tiny loss, compared to sulphation which would eat up battery capacity a lot faster if it would be allowed to sneak in.

cheers, Peter

Hi Ian,

Now I don't profess to know everything about solar and batteries but I was wondering if the regulator is setup properly. I know you can set the max voltages on some of the better ones. Perhaps this needs to be changed, perhaps the batteries when on solar get up to the limit set by the regulator and stop charging. Just a thought. I know with my AGM 75A/H Thumper that 12.75V = 100% but while charging it can get up to 13.xxV and when using the solar panels the regulator can show the voltage at even 14.xxV.

Not sure if I've helped any or just added confusion.

Robyn

Hi Peter,

You say here that 14.5v should be limited to a few hours a day. There must be thousands of us who have aux batteries / campers / van batteries getting charged on the run from the vehicle battery & alternator. These are pushing out above 14v while the engine is running, often for many hours.

Are you suggesting that we are slowly killing our aux batteries by this method of charge on the run?

thanks,

I've got 3 x Ritar 100 Ah AGM's in my van (using a Prostar solar controller and Ctek mains charger). When new, the batteries often got to 14.8V on mains charging but would soon be back down to the high 13's when the charger was off. Now after 3 years, about 14.2 seems the max on charge and 13V comes quickly when turned off (as Sandy says though, the post-charging V is the one of interest - and as you say, the V on draw is the vital figure). My voltage levels are falling sooner now that the batteries are aging. My solar controller and Ctek charger are still configured as set by the installer at the van factory, but I've been over the manuals and the setup seems ok to me (but I am an electro-klutz of sorts). We have 2 x 130W Kyocera panels and a small gennie for top ups. When the service period becomes practically too short, I guess new batteries are indicated. I've been researching them lately and the prices for quality seem very scary.

Lets clear up a few false notions.

A battery is not a bucket, it is a chemical system, and the notion of "FULLY CHARGED" in my opinion is a contrived one.

There are approximate voltage figures that indicate "state of charge".

These figures are only valid with the battery at a resting state, not being charged, not being discharged and having been that way for some time.

These figuers are temperature dependent and there are slight variations dependent on battery chemistry.
While more or less reliable thay are far from absolute.

There is no fixed and relaible measure of battery capacity and state of charge is likewise a fluid concept.

People want to think their battery is like a bucket and there are plenty out there that will sell to that desire.

Moving on.

To charge a battery we have to apply a voltage higher than its resting terminal voltage otherwise no current will flow and no charging will occur.....

We charge a battery with a higher volatge than its resting voltage..after we remove that charging voltage the battery will take some time to settle back to a resting state.

Now this is where some will argue about what is "Fully Charged"...if we charge a nomonal battery with a nominal voltage like 13.8 volts once universally considered the optimum long term charging voltage.
The battery will reach a state of "charge equalibrium" where the battery is accepting no more charge and any current flowing is wasted or lost ( no drama).
Your conventional nominal battery will not excessivly gass nor loose excessive water.
This battery would have once been considered "FULLY CHARGED" and would settle back to 12.5 ish volts, and if it is healthy it will hold that for weeks or months if left alone.

There have been some changes in battery chemistry and some changes in what people are saying.
many would now claim that that battery was not fully charged and recomend charging at a higher voltage to get that battery "FULLY CHARGED"

Now the terminal voltage may settle to 12.8 volts ( or whatever) after this....but in the long term over a couple of hours or so ( even a day) the battery will still settle to arround 12.5 volts and stay there if healty and left alone.

In my opinion it has been over charged, not in a problematic way, but over charged all the same, because it will settle over time.

NOW
with the addition of calcium to batteries and changes in acid chemistry, some of the charging voltages have changed..and lots of things are misunderstood.

Especially sulphation.
One of the chief causes of sulphation is overcharging.

I do not believe for a minute that charging your battery at a higher voltage each day will reduce sulphation....the opposite actually

Keeping your battery cool will reduce sulphation
Not allowing your battery to remain under charged will reduce sulphation.
Minimising deep cycling will reduce sulphation.
Charging your battery at the optimum and expedient rate will reduce sulphation.
Using a charger withn a pulsed antisulphation program will reduce sulphation
Not regularly over charging your battery will reduce sulphation.

As for various batteries being regularly charged with higher voltages reducing their life......damn tootin' it will.......but don't get bent out of shape over it...elivated underbonnet temperatures probably do more damage to car batteries.....especially AGM and other sealed batteries.

13.8 volts will still fully charge any of the lead acid battery family, but it may take some time.

The only time it is necessary to charge a battery at the higher voltages is to overcome charge resistance that some batteries can develop or to speed the charging rate.

If you have a good quality modern charger or regulator it should do all this for you.

Don't get bent all out of shape over all this, you could worry all you want about ya batteries an not add a single hour to their short lives.

As for what is optimum for an individual battery......there is a great variation in small things with what is being done with batteries....consult the manufactures specifications for that model of battery.

cheers

your are right bantam, but the concept of the battery being a bucket, and voltage being water pressure, and wires being a hose, and amps being how much water is flowing... (you get me?)is one that gets the concept across to many people.

situations such as resting state, surface charge etc etc cause many eyes to glaze over!