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.
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 21 May 2004 15:07:58 GMT, (Gould 0738) wrote:

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

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

There is a great deal of logic however in saying that 12.6 is the
normal resting voltage of a fully charged battery. That is the
condition most people will be interested in. Evaluating the state of
charge of a battery still connected to a charger/eliminator makes very
little sense, and that is really what this whole discussion is all
about.

"Wayne.B" wrote in message
...
On 21 May 2004 15:07:58 GMT, (Gould 0738) wrote:

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

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

There is a great deal of logic however in saying that 12.6 is the
normal resting voltage of a fully charged battery. That is the
condition most people will be interested in. Evaluating the state of
charge of a battery still connected to a charger/eliminator makes very
little sense, and that is really what this whole discussion is all
about.


This is the point I was trying to politely make to Gould. If you listen to
his story half the newbie boaters will be filing into West Marine to buy new
batteries when the ones they have are likely to be perfectly fine.

Eisboch

This is the point I was trying to politely make to Gould. If you listen to
his story half the newbie boaters will be filing into West Marine to buy new
batteries when the ones they have are likely to be perfectly fine.

Eisboch

Your point is accurate, merely incomplete and also misleading if considered
without
taking important variables into account.

If that "newbie" owns a battery that cannot be charged to a point above 12.6
volts on a functional charger he darn well just might be in need of a new one.

Do most boaters disconnect the battery from the boat, and set it on the dock
overnight, before evaluating the state of battery charge? If we are going to
discuss
testing a battery and the results that should be expected, it makes sense to
frame that discussion around actual boating conditions.

What happens when the "surface charge"
bleeds off a battery that can only absorb 1.1 volts per cell? Probably drops
down close to 12 volts in fairly short order- a marginal level that all of us
will agree is getting rather weak.

There's also a difference in the voltage one can expect if checking the
batteries on a trailer boat sitting in the backyard under a tarp vs a boat that
is connected to shorepower. But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on it may
read less.

"Gould 0738" wrote in message
...


But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on
it may
read less.


Awesome! We agree.

Thanks

Eisboch

"Gould 0738" wrote in message
...

Do most boaters disconnect the battery from the boat, and set it on the
dock
overnight, before evaluating the state of battery charge?

If you want to establish state of charge based on voltage alone then that is
what you should do. It doesn't have to be overnight, but an hour would be a
good idea.

If the battery is not at rest then you have to consider the current along
with the voltage, which makes things a lot harder. A battery at rest will
NOT be at 13.2 volts. A battery charger will "float" a battery at around
13.2 volts, and IF the battery is fully charged there will be little or no
current flow into the battery. If you measure the battery voltage when it
is connected to a charger then you need to verify that the current is near
zero before you can say that the battery is fully charged.

Rod

"Gould 0738" wrote in message
...
This is the point I was trying to politely make to Gould. If you listen to
his story half the newbie boaters will be filing into West Marine to buy new
batteries when the ones they have are likely to be perfectly fine.

Eisboch

Your point is accurate, merely incomplete and also misleading if considered
without
taking important variables into account.

If that "newbie" owns a battery that cannot be charged to a point above 12.6
volts on a functional charger he darn well just might be in need of a new one.

A bad battery or a depleted battery may still read a high voltage when connected
to a charger, and even for a while after being removed. All your reading of
13.2 tells you is that your charger decided to go into float mode. This may be
a strong hint that the battery is fully charged, but it doesn't necessarily mean
that.


Do most boaters disconnect the battery from the boat, and set it on the dock
overnight, before evaluating the state of battery charge?

If you read the information I presented, you would know that a flooded battery
will settle most of the way rather quickly, and that the surface charge can be
removed by applying a load for a few minutes. Every boater should learn these
simple facts, it isn't rocket science.

If we are going to discuss
testing a battery and the results that should be expected, it makes sense to
frame that discussion around actual boating conditions.

What could be more of an "actual condition" than checking the state of charge
when you wake up after a night on the hook? Your scenario seems to be connected
to shore power. Further, if someone is interested in getting a reliable State
of Charge, they should use the methods described by all of the experts. It only
takes a few minutes to remove a surface charge; failure to do so gives a
meaningless answer.



What happens when the "surface charge"
bleeds off a battery that can only absorb 1.1 volts per cell? Probably drops
down close to 12 volts in fairly short order- a marginal level that all of us
will agree is getting rather weak.

I'm not sure what you mean by "absorb 1.1 volts" - batteries absorb Amps, not
Volts. But yes, if a battery is reading 12 Volts with no load, it is probably
either discharged or in poor health.


There's also a difference in the voltage one can expect if checking the
batteries on a trailer boat sitting in the backyard under a tarp vs a boat
that
is connected to shorepower. But in either case, at the moment when the battery
has absorbed a full and healthy charge or recharge it will
read 2.2 volts per cell. I don't disagree with a statement that later on it
may
read less.

This may be true with a given charge protocol, but it is not true in all cases.
Further, the opposite is not true at all: if you get a reading of 13.2 without
having any knowledge of the history, you can't say anything about the charge
state or the general health of the battery. This is the essential point in this
discussion. If a battery is discharged to 80%, and then you put it on a float
charger at 13.2, you won't add much (if anything) to the charge state, but
because of the surface charge you will get a reading of 13.2.

Anyone interested in learning about this should read the links I've provided, or
google on: "surface charge" battery

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.