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From: Mark Olson on 1 Dec 2009 16:56
Bob Myers wrote:
> S'mee wrote:
>>> Battery manufacturers would disagree slightly.
>>>
>>> If you charge up a sealed AGM battery, you may read
>>> 14 ~ 15 volts when you first take it off the charger, but the resting
>>> voltage will drop down to 12.8 volts and stay there in about half an
>>> hour, assuming that the battery was in good condition and took a full
>>> charge.
>> If you posted it it's either a LIE or you plagerized it...
>
> He no doubt did a cut-and-paste of this info, but at
> least this time he used a source that was correct. Per the
> basic chemistry, one lead-acid cell should provide a
> nominal voltage of somewhere around 2.1, so for
> a six-cell-in-series battery, you should see somewhere
> around 12.6V. The "13.X" volt reading that we're used
> to seeing in charging situations (including what you'd
> see on a voltmeter on your car dash, since presumably
> the engine is running and the system is in the "charging"
> condition when you'd see this) is because you have to
> use a slightly higher voltage per cell to charge the thing.
> But 14-15V is high; exceed about 2.4 V/cell (14.4V across
> a "12V" six-cell battery, and a lead-acid cell will start
> outgassing. Typically, a charger is set to deliver something
> like 2.2-2.3 V/cell, or 13.2-13.8V across the battery - and
> that's the highest you should ever be reading across the
> battery terminals.

Mostly correct if you are talking conventional lead-acid batteries, but
for many new bikes that come with sealed VRLA (valve regulated lead acid)
batteries, the lead-calcium chemistry is different, and the voltages are
a little higher. According to Yuasa,

When considering upgrading to a sealed VRLA
battery that did not come OE in your vehicle, check
to make sure your charging system has a
regulated output between 14.0 - 14.8v.

Of course this applies to vehicles that came from the factory with sealed
VRLA batteries too, not just older vehicles that are being retrofitted.

Also, the _fully_ charged voltage of a sealed VRLA battery is 13.0V, not 12.6V:

Check voltage using a voltmeter. Readings for a charged, newly-activated
battery should be 12.8v or higher after the battery is charged and sits for
at least 1 - 2 hours. If less, it needs an additional charge.

I strongly recommend that anyone who has an interest in taking the best
possible care of their motorcycle battery, no matter what style or type,
to download and read Yuasa's excellent technical manual.

http://www.yuasabatteries.com/pdfs/TechMan.pdf

It has enough detail and enough plain language to satisfy both picky chemists
and curious ignotes.




From: Bob Myers on 1 Dec 2009 17:19
Mark Olson wrote:
> Mostly correct if you are talking conventional lead-acid batteries,
> but for many new bikes that come with sealed VRLA (valve regulated lead
> acid) batteries, the lead-calcium chemistry is different, and the
> voltages are a little higher. According to Yuasa,

I stand (well, sit) corrected, or at least amended, however
please let me add that "VRLA" does not necessarily imply
a different cell chemistry (the name itself simply means
"valve-regulated lead-acid," and refers to any of the
construction types where the battery is "sealed" and will not
vent excess gas until/unless a pressure relief valve is triggered.
These are also generally classed as "acid-starved" and/or
"recombinant" types, as they (a) generally contain less acid
than a conventional design, and (b) are constructed such that
generated hydrogen and oxygen gases will recombine rather
than vent, as long as the pressure remains below the relief
valve's trip point. However, while this permits a somewhat
higher charge voltage (and therefore faster charging) to be
safely used, the cell chemstry is very often exactly the same
as in conventional types, and so the voltage of a charged
cell or battery would in those cases also be the same. So
in the case of a VRLA type, you will often see somewhat
higher charging voltages, but the same voltage as in a conventional
type when you simply check the battery voltage on its own.

In any event, we certainly agree that one should not exceed
the recommended maximum charging voltage per the
battery manufacturer's recommendations; Bad Things can
happen if you do. 15V is high for any of these types.

Bob M.



From: Mark Olson on 1 Dec 2009 18:11
Bob Myers wrote:
> Mark Olson wrote:
>> Mostly correct if you are talking conventional lead-acid batteries,
>> but for many new bikes that come with sealed VRLA (valve regulated lead
>> acid) batteries, the lead-calcium chemistry is different, and the
>> voltages are a little higher. According to Yuasa,
>
> I stand (well, sit) corrected, or at least amended, however
> please let me add that "VRLA" does not necessarily imply
> a different cell chemistry (the name itself simply means
> "valve-regulated lead-acid," and refers to any of the
> construction types where the battery is "sealed" and will not
> vent excess gas until/unless a pressure relief valve is triggered.
> These are also generally classed as "acid-starved" and/or
> "recombinant" types, as they (a) generally contain less acid
> than a conventional design, and (b) are constructed such that
> generated hydrogen and oxygen gases will recombine rather
> than vent, as long as the pressure remains below the relief
> valve's trip point. However, while this permits a somewhat
> higher charge voltage (and therefore faster charging) to be
> safely used, the cell chemstry is very often exactly the same
> as in conventional types, and so the voltage of a charged
> cell or battery would in those cases also be the same. So
> in the case of a VRLA type, you will often see somewhat
> higher charging voltages, but the same voltage as in a conventional
> type when you simply check the battery voltage on its own.

No, according to Yuasa, that is not the case with their sealed VRLA
batteries. Perhaps it is true of other makes, but I doubt it.

> In any event, we certainly agree that one should not exceed
> the recommended maximum charging voltage per the
> battery manufacturer's recommendations; Bad Things can
> happen if you do. 15V is high for any of these types.

I'm not a chemist nor do I play one at weekends, but if you read the
Yuasa technical manual, I think all or most of your concerns about
sealed VRLA batteries and their electro-chemistry will be addressed.
I strongly doubt that any VRLA batteries sold to the general public are
anything other than a lead-calcium chemistry. Here's what Yuasa has to
say about their sealed VRLA batteries:

1. The plates are comprised of special lead-calcium
alloy grids and charged active material. Lead-calcium
reduces self-discharge – the battery holds its charge
longer. The construction of the sealed VRLA battery
causes freed gas to recombine inside the battery instead
of being vented… allowing the battery to be sealed.

....

During discharge, sulfuric acid electrolyte solution reacts
with the lead plates, turning them into lead sulfate. The
electrolyte – sulfuric acid solution made up of hydrogen,
sulfur and oxygen – gives up its sulfur and some of its
oxygen and turns to water.

PbO2 + Pb + 2 H2SO4 → 2 PbSO4 + 2 H2O

The process reverses with charging. Electrolytes and
plates return to their original composition. The charging
current breaks down water into its component gases:
hydrogen (from the negatively charged plate) and oxygen
(from the positive plate). Gases escape out the vent
tube. With a conventional battery, water is added to
replace that loss.

Here's the real secret of a sealed VRLA battery: the negative
plate never becomes fully charged… so, no hydrogen
gas. The positive plate still makes oxygen, but instead of
being forced out the vent tube, it reacts with the charged
active material to become water again. That's “gas
recombinant technology.” That's the magic of YUASA's
non-spillable, sealed VRLA battery.

Really, download that PDF and read it, I found it fascinating.
From: paul c on 1 Dec 2009 19:07
Mark Olson wrote:
....
> I strongly recommend that anyone who has an interest in taking the best
> possible care of their motorcycle battery, no matter what style or type,
> to download and read Yuasa's excellent technical manual.
>
> http://www.yuasabatteries.com/pdfs/TechMan.pdf
>
> It has enough detail and enough plain language to satisfy both picky
> chemists
> and curious ignotes.

Thanks for that link. It mentioned another Yuasa pub'n that I hadn't
seen before:

http://www.yuasabatteries.com/pdfs/2009_yuasa_apps_specs.pdf

Has cross-reference for some other mfrs' batteries, plus the suggested
Yuasa batteries for a lot of bikes going back for years. Come to think,
for years I've abused their batteries too, with generally better results
than I deserved.

(I don't know if there is another powersports battery company like Yuasa
in North America who are so forthcoming with their information, maybe
they are just better at knowing their market. I remember seeing a
really nice tester they made but it was a bit too much for my
pocketbook. Would have bought one of their chargers if it had been
readily available locally.)
From: Mark Olson on 1 Dec 2009 21:46
paul c wrote:

> (I don't know if there is another powersports battery company like Yuasa
> in North America who are so forthcoming with their information, maybe
> they are just better at knowing their market. I remember seeing a
> really nice tester they made but it was a bit too much for my
> pocketbook. Would have bought one of their chargers if it had been
> readily available locally.)

I love it when companies give you extensive specs and tech information.
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