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"Gould 0738" quoted in message

...

a bunch of theoretical mumbo jumbo from:

http://www.av8n.com/physics/lead-acid.htm

Ok, Chuck. Next time you need a new battery for your boat, run down to West
Marine and ask for a 13 volt battery.

More volts to you!

Eisboch (happy to have 12.6 when I can get it)

An informed reference citing that voltage in a lead acid battery should not be
allowed to "fall below" 2.1 volts per cell.

http://www.batteryuniversity.com/partone-6.htm

(Rather a long way from jam-packed to capacity at the same value).

A source with yet a third opinion:
Describes a fully charged cell as 2.17 volts, float voltage at 12.9.

http://www.keelynet.com/energy/sylcell.htm

Yet another opinion:

"2.15 volts per cell."

Includes a chart showing a 12-volt battery is about 25% discharged at 12.6
volts

http://continuouswave.com/whaler/ref...geBattery.html

An SLA must always be stored in a charged state. A topping charge should be
applied every six months (or other time intervals as recommended by the
manufacturer) to avoid the voltage from dropping below 2.10 volts per cell.

An approximate charge-level indication can be obtained by measuring the open
terminal voltage of the cell while in storage. A voltage of 2.11V reveals that
the cell has a charge of 50% and higher. If the voltage is at or above this
threshold, the battery is in good condition and only needs a full charge cycle
prior to use. If the voltage drops below 2.10V, several discharge/charge cycles
may be required to bring the battery to full performance.

(from)

http://www.allegromicro.com/techpub2.../index3311.htm

*******************

2.11 volts per cell indicates as little as a 50% charge, according to this
source

"Gould 0738" wrote in message
...
Yet another opinion:

"2.15 volts per cell."

Includes a chart showing a 12-volt battery is about 25% discharged at 12.6
volts

http://continuouswave.com/whaler/ref...geBattery.html

I see where you are coming from Chuck. I think our differences are real
world vs theoretical.
Once discharged, even modestly, a brand new battery cannot be charged back
to and hold (without benefit of a float charger) it's theoretical capacity.
Initially the difference is small, but over time and with subsequent
discharges, the difference gets larger until it's time for a new battery.
During it's lifetime, the battery is considered "good" even though it is
slowly degrading. Equalization or reconditioning extends the useful life of
the battery, but it can never achieve and hold the theoretical per cell
charge. To make matters worse, I doubt you could find a mass produced
battery that has each cell producing exactly the same voltage, and more so
as the battery ages.

A couple of years ago I had to replace three 8D batteries in my big boat.
Since I didn't want double hernias from this process, I checked the voltage
on the new batteries before lugging them down into the engine room. 12.6
volts on each.

I guess we exhausted this subject.

Eisboch

Of lot of interesting links. Of course, none are relevant to the discussion.
For example, much of it refers to SLA batteries, what here in the States are
usually called Gel batteries. Admittedly, their "open circuit voltage" is
higher: 13.0 Volts is considered 100% charged, and 12.6 would be roughly half
discharged. Further, the settling time is considerably longer.

However, for a normal flooded battery an open circuit Voltage of over 12.6 to
12.8 (depending on the model) implies 100% charged. As Nigel Calder says "If
Voltage readings are to be a meaningful reflection of the state of charge, the
battery must be allowed to sit for at least 10 minutes; and hour or two would be
better, overnight would be best (gel-cell batteries may to 48 hours to
stabilize)." He then refers to a chart that indicates 100% charged for 12.6
Volts or greater (typical wet-cell);13.0 (Gel-Cell).

A fuller description at:
http://www.optimabattery.freeserve.c...AQ/carfaq4.htm
where it explains that "Surface charge is the uneven mixture of sulfuric acid
and water along the surface of the plates as a result of charging or
discharging. It will make a weak battery appear good or a good battery appear
bad." In other words, of you read the Voltage immediately after removing the
charger, you will be misled as to the state of charge.

You mentioned you have Rolls Batteries. Here's their service bulletin, where
they say "Determining state of charge by voltage is more difficult as there must
be no load or surface voltage present", but they indicate 100% charged is at
12.6 Volts:

http://www.rollsbattery.com/Bulletins/600.htm

"Gould 0738" wrote in message
...
An SLA must always be stored in a charged state. A topping charge should be
applied every six months (or other time intervals as recommended by the
manufacturer) to avoid the voltage from dropping below 2.10 volts per cell.

An approximate charge-level indication can be obtained by measuring the open
terminal voltage of the cell while in storage. A voltage of 2.11V reveals that
the cell has a charge of 50% and higher. If the voltage is at or above this
threshold, the battery is in good condition and only needs a full charge cycle
prior to use. If the voltage drops below 2.10V, several discharge/charge
cycles
may be required to bring the battery to full performance.

(from)

http://www.allegromicro.com/techpub2.../index3311.htm

*******************

2.11 volts per cell indicates as little as a 50% charge, according to this
source

Of lot of interesting links. Of course, none are relevant to the discussion.

The discussion question revolves around the voltage of a fully charged battery.

When evaluating battery charge to determine whether the charger has done its
job, the voltage you want to achieve is 2.2 volts per cell, or 13.2.

If you are disconnecting a charger when you get to 12.6, you have not fully
charged your battery. If your charger cannot raise the voltage above 12.6, you
have a bad charger or a failing battery.

Several hours later the state of charge may deteriorate from 13.2 to 12.6. Your
quote from Nigel Calder says that it might take as long as "overnight" for the
battery to self-discharge to 12.6.

The final .6 volts are there in the beginning, when the battery is *fully*
charged, and before it drops off to the lower number.
Therefore, a fully charged battery is 13.2 unless the final .6 volts can be
shown to be a mass hallucination.

There is no logic at all in a position that says the battery is not "fully
charged" until the reading declines .6 volt.

On Fri, 21 May 2004 10:32:00 -0400, "Jeff Morris"
wrote:

You mentioned you have Rolls Batteries. Here's their service bulletin, where
they say "Determining state of charge by voltage is more difficult as there must
be no load or surface voltage present", but they indicate 100% charged is at
12.6 Volts:

http://www.rollsbattery.com/Bulletins/600.htm

===========================================

The Rolls web site information is right on the money in my experience.

If memory is correct, Rolls was founded by John Surette who has long
been regarded as a leading battery engineer.