Do you beleive these stats on Battery Voltages?

 


Battery Voltages
    Because batteries are always referred to as 12-volt (or 6V or 24V),
it is often assumed that the normal voltage is 12V. In fact a
12V lead-acid battery only producing 12.0V is either
almost flat or is delivering a large current (under a heavy load).
In fact, a healthy 12V battery, when not being charged,
should always show 12.2 - 12.8V.

    Very conveniently, the relationship between a battery's state
of charge and its voltage is linear (10% per 0.10V) between about 90%
(12.70V) and 20% (12.0V). However, when a battery has been on
charge, even if its not fully charged, the voltage will be up
around 13.8V. This will slowly drop to around 13.6V over the next
few hours, but even if left overnight it shouldn't drop below
13.0V unless the battery was only partly charged or is on the way out.
    But, as soon as a reasonable sized load is switched on, the voltage
drops quite quickly until it equates to the battery's actual
state of charge. Thereafter, the rate of voltage change (under
constant load) becomes linear. Thus, in practice, the voltage
of a freshly charged battery is a poor guide to its state of charge
until some of the charge has been used.

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

    If the part about (will slowly drop to around 13.6V over the next
few hours) is still true for small m/cycle batteries, and is not RC/Ah
specific, then I've been getting ripped of on some of the "wet' sla GS/Yuasa
batteries I've been buying..

    I know, even the "agm" Chinese batts can hold these stats, but even
13.6 volt  "agm" is a drag to start, whereas  even a 12.6v "wet" will snap
start better.

    The Chinese "agms" seem more like a "gel" battery rather than a
Starting Battery, I think an AGM with cell vent cap holes is pretty unreal
and may just be a bunch of sponge mixed with a sulphuric acid solution,
rather than a real AGM,which is much different...and Concorde pricier.

Bob

 


Krusty's sockpuppet troll. also trying to hide...poorly. "groups:
poster"

 



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.

 

On Sat, 28 Nov 2009 09:52:20 -0800 (PST), âÍÁ Á³Õ »Ñ·àÁ ËØÁ

|>
|>> Very conveniently, the relationship between a battery's state
|>> of charge and its voltage is linear (10% per 0.10V) between about 90%
|>> (12.70V) and 20% (12.0V). However, when a battery has been on
|>> charge, even if its not fully charged, the voltage will be up
|>> around 13.8V. This will slowly drop to around 13.6V over the next
|>> few hours, but even if left overnight it shouldn't drop below
|>> 13.0V unless the battery was only partly charged or is on the way out.
|>
|>Battery manufacturers would disagree slightly.
|>

Yer sure right about that, it's a 3 ring circus of dis/informations all
over.
    It may depend on were they were made, but I did use some Chinese
"AGMs" with a holding 13.6 volts 2 hours after charging but no load....it
started with about the same cca as a 12.8 "wet" sla battery.
 
|> 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.


This battery is on the vehicle circuit, and not a stand alone battery on a
table....right?....a GT9B-4 12v/8Ah wants a charge at 12.v, and the Majesty
Yamaha yp400ts manual considers 12.8v as a minimal voltage, but AGMs can go
down to 12.5v before needing a recharge.
 
    I prefer using a Shumacher 4 stage smart charger with blinding LEDs,
and it equalise/bulk/absorb charges to 12.9v/%100 and then goes into a float
maintenance mode, and goes up to a possible 17v (stubborn batt) to maintain
at least a 13.2v for regular MF/Marine/DeepCycle, and 13.4v for agm/gel
status for a specified time.
    The 12.9v full charge is referred as %90 by other chargers, most
chargers, all have a slightly different but very consistent preference.
.
    This float *topping mode* is good if you have time/patience with a
passive/auto smartcharger....wereas an active/constant charger  feeds the
battery what it is supposed to be with no time consuming battery queries.

Bob

 



No, that is the open circuit voltage while the battery is sitting on
the table half an hour after charging it.

The manufacturer's literature that comes in the box with the battery
tells exactly how to fill it with the supllied electrolyte and how
long to charge it and at what rate.

Then the literature says to measure the resting *open circuit* voltage
and specifies that 12.8 volts indicates a full charge for the AGM
battery.

If the manufacturer doesn't know the right information, who on earth
would know?

If I can't trust the manufacturer to give me correct information, then
I'm at their mercy...

The last two AGM batteries I've owned lasted 8 years without problem.