Download How to Charge an AGM Battery

How Do I Pick a Battery Charger!
By Batterycharger.com
Let me start with a disclaimer; BatteryStuff.com does not sell inexpensive off the shelf chargers
such as the type often found at retail outlets and certain other online stores. We cater specifically
to microprocessor controlled chargers, also known as Smart Chargers. All the chargers we stock
are reviewed, tested, and selected based on function, reliability and durability. These chargers are
designed to charge lead acid and other types of batteries based on computer generated
algorithms. Simply put, the charger collects information from the battery and adjusts the charge
current and voltage based on this information. This allows the battery to be charged quickly,
correctly, and completely when using a smart charger. All The chargers we sell can remain
connected to the battery(s) indefinitely and will not overcharge or damage your battery(s).
Here are some simple steps to aide you in selecting the correct charger for your needs.
Step 1
Determine what type of battery or batteries you will be charging. Maintenance Free, Wet Cell
(flooded), AGM (absorbed glass mat), Gel Cell or VRLA (valve regulated lead acid). In most
cases one charger will work for all types except for Gel Cell. However, some of our Gel Cell
chargers will work well with the other battery types.
Step 2
What size is your battery? What we mean is not physical size, but how many
Amp hours does your battery store. As an example, a typical full size auto battery is about 50
amp hours, and it would take a 10 amp charger approximately 6 hours to recharge it if the battery
were completely dead. Another example, a Marine Deep Cycle Battery may be rated at 100 amp
hours, so it would take a 10 amp charger about 11 hours to recharge a dead battery to near 100%
full charge, from a completely discharged condition. To calculate your total charge time, a good
rule of thumb is to take the amp hour rating of the battery and divide by the charger rating
(amps) and then add about 10% for the extra time to totally top off the battery.
Some folks need to size the charge for quick recharge, therefore requiring more amps from their
charger. Others are not in a hurry and may select a smaller charger. The most important thing
here is to make sure you have enough charger power to do the job you require in the time you
allocate.
Step 3
Know your desired outcome. Some folks require a charger to keep their
motorcycle, classic car, or aircraft battery charged during the off season. In such a case a simple
low current charger will work fine. Others require a fast and powerful charger to quickly restore
a trolling motor battery or a wheel chair battery set.
There are certainly other factors in selecting a battery charger, and it would be difficult to cover
them all, but here a few. Input voltage, generally for use foreign countries. Exposure to elements,
i.e. would you benefit from a waterproof charger? Perhaps you will need a charger that doubles
as a power supply for a RV or some other application. Often people will need to charge multiple
batteries simultaneously, so multiple bank chargers may be needed.
Following is a list of definitions of different types of batteries and their uses.
Flooded:
This is the traditional engine start, tractor and deep cycle style battery. The liquid electrolyte is free to
move in the cell compartment. The user has access to the individual cells and can add distilled water as
the battery dries out. Popular uses are engine starting and deep cycle designs.
Typical absorption voltage range 14.4 to 14.9 volts, typical float voltage range 13.1 to 13.4 volts.
Sealed:
This term can refer to a number of different constructions, including only a slight modification to the
flooded style. In that case, even though the user does not have access to the cell compartments, the
internal structure is still basically the same as a flooded battery. The only difference is that the
manufacturer has ensured that a sufficient amount of acid is the battery to sustain the chemical reaction
under normal use throughout the battery warranty period. Other types of lead acid batteries are also
sealed, as explained below. Very popular uses are engine start and limited starting/deep cycle
applications.
Typical absorption voltage range 14.2 to 14.7 volts, typical float voltage range 13.1 to 13.4 volts.
VRLA:
This stands for Valve Regulated Lead Acid battery. This is also a sealed battery. The valve regulating
mechanism allows for a safe escape of hydrogen and oxygen gasses during charging.
Typical absorption voltage range 14.2 to 14.5 volts, typical float voltage range 13.2 to 13.5 volts.
AGM:
The Absorbed Glass Matt construction allows the electrolyte to be suspended in close proximity with the
plates' active material. In theory, this enhances both the discharge and recharge efficiency. Actually, the
AGM batteries are a variant of Sealed VRLA batteries, just a more advanced design. Popular usage
includes high performance engine starting, power sports, deep cycle, solar and storage battery.
Typical absorption voltage range 14.4 to 15.0 volts, typical float voltage range 13.2 to 13.8 volts.
GEL:
The Gel cell is similar to the AGM style because the electrolyte is suspended, but different because
technically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica
additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the
other styles of lead acid battery. This is probably the most sensitive cell in terms of adverse reactions to
over-voltage charging. Gel Batteries are best used in VERY DEEP cycle application and may last a bit
longer in hot weather applications. If the incorrect battery charger is used on a Gel Cell battery poor
performance and premature failure is certain. Battery chargers with gel profile will have information
either on the unit, or in the manual, about gel compatibility.
Typical absorption voltage range 14.0 to 14.2 volts, typical float voltage range 13.1 to 13.3 volts.
Note about Gel Batteries: It is very common for individuals to use the term GEL Cell when referring to
sealed, maintenance free batteries, much like one would use Kleenex when referring to facial tissue or
"Xerox machine" when referring to a copy machine. Be very careful when specifying a charger. More
often than not, what someone thinks to be a Gel Cell is really a sealed, maintenance free, VRLA or AGM
style battery.
How to Charge an AGM Battery - How to Do It
HOT ROD Untangles A Mystery: How To Bring An AGM Battery Back From The
Dead. Before You Replace That Expensive Piece, Try This.
By Bill McGuire, Photography by Bill McGuire
Hot Rod Magazine, September, 2010 Read more at:
http://www.hotrod.com/techarticles/general/hrdp_1009_how_to_charge_a_agm_battery/viewall.html#ixzz2QAO
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As part of its HOT ROD torture test, this Optima AGM battery was deliberately dealt a long, slow, 2.2-amp discharge until it
showed less than 4 volts across the terminals. At reduced voltage levels, many conventional battery chargers will refuse to deliver
an effective charge-producing the frequent complaint that an AGM battery "won't take a charge." In reality, the battery simply
has insufficient potential for the charger to "see" it in the circuit.
At HOT ROD, we hear stuff. Lately we've been hearing about hot rodders' love/hate relationship with
their sealed, leak proof batteries. You adore their ability to take punishment and their paint-friendly
nature, but they have developed a reputation for refusing to take a charge once they have gone dead.
Here's how to bring them back to life.
First, some background. While the spill-proof batteries currently on the market are often referred to as gel
batteries, most are AGM batteries-short for absorbed glass mat. Optima and Odyssey batteries are
common examples. Unlike a gel battery, in which a silica agent is added to the electrolyte to form a
semisolid, an AGM battery uses an ordinary sulfuric acid solution like any standard automotive battery
(about 60/40 water and acid at full charge). However, here the electrolyte is absorbed and retained by
layers of boron-silicate glass matting between the lead plates. While both battery types can rightly be
considered leak proof and spill-proof, AGM is currently considered the superior technology, especially
for automotive use. Some AGM batteries employ spiral-wound, cylindrical cells (Optima), while others
use flat plates and box cells (Odyssey) like conventional batteries. Also, sealed is something of a
misnomer-lead-acid batteries generally are capable of venting when necessary.
Here's the magic fix: When an AGM battery won't charge by ordinary means, simply connect a second, well-charged battery
(12.4 volts or greater) in parallel with the dead unit-positive to positive, negative to negative. Then connect the charger to the
pair. This will in effect trick the charger into delivering the necessary current to the discharged battery. Using this method, we
brought several deep-discharged batteries back to life. By the way, this trick also works with conventional batteries, though it's
not quite as effective. For maximum battery life, Optima advises that normal charging should be limited to 10 amperes. Other
manufacturers advise similar limits. So-called sealed batteries can be especially sensitive, but in no case should any automotive
battery be allowed to heat significantly while charging. Excessive charging current and temperatures will age a battery before its
time and can even be dangerous. When you overcharge a battery, essentially you are manufacturing hydrogen.
Hot rodders are tough on batteries, but the extreme heat and vibration we deal them isn’t the half of it.
Between these rounds of serial abuse, often we let our cars sit unused for extended periods-like between
race events or cruise nights, or even for the entire winter. Also, the electronic gadgets in newer cars
(engine and body computers, entertainment and security systems, and so on) often employ keep-alive
memory functions that place a small but constant current draw on the battery.
That's an awful thing for automotive batteries, because they all will self-discharge over time-even the
more expensive deep-cycle models (just more slowly). At room temperature, a standard battery loses
nearly 5 percent of its capacity per month just sitting on the shelf. And once the battery's voltage falls
below around 1.75 volts per cell, permanent damage begins to take place in a process known as hard
sulfation. Essentially, the plates become coated with gunk (dense lead sulfate crystals), reducing the
battery's capacity. If a battery is allowed to discharge long enough or not properly recharged between
discharges, it's a dead player. Its plates are completely sulfated and nothing will bring it back.
Some AGM batteries, like the Optimas shown here, use spiral-wound plates in cylindrical cells-hence the six-pack appearance.
Among other things, spiral-wound cells allow purer lead to be used in the plates, it is claimed, since they need not support their
own mass. Other AGM makers say conventional construction is superior, claiming greater plate area for a given case volume. In
the Optima line, the Red Top is the performance piece, while the Yellow Top is a dual-purpose battery for both performance and
deep-cycle use. (A race car with no charging system would be an ideal application.) A dark-gray case denotes a conventional
Optima battery, while light gray indicates a deep-cycle model. Deep-cycle batteries deliver lower peak current but can withstand
deeper discharges. A Blue Top Optima is for marine applications. It will start your car but is not optimized for automotive use.
To replicate these diabolical conditions, we obtained two new Optima AGM batteries, a standard Red Top
and a deep-cycle Yellow Top model, and submitted each to a constant 2.2-ampere load. At regular
intervals over many days, we removed the load and attempted to recharge the batteries using a standard,
repair industry-style, 2/10/40-ampere, roll-around charger, known in the biz as a bulk charger. At no point
did we have any trouble getting either battery to accept a charge-that is, until the around-the-clock
discharge drove the batteries below around 4.2 volts. Then the batteries refused to charge, replicating the
common complaint-"won't take a charge."
However, the trouble isn't really with the battery or even, necessarily, the charger. Here's the real
problem: Once the battery's voltage falls below a certain level, the charger can no longer sense the
battery's presence and will refuse to deliver the current. In some cases this can occur at any point below
10.5 volts. Older and more basic chargers are more prone to this hang-up than newer, fancier models,
which are equipped with control circuitry to deal with these issues. So there are two solutions available:
Buy a new, expensive charger equipped with the extra brainpower, or employ a simple trick the Optima
engineers laid on us.
For maximum model coverage, many aftermarket batteries are equipped with top and side terminals, and there is no reason you
can't use them both. In fact, battery manufacturers recommend that you connect the vehicle's main cables to the side terminals in
high-load applications, then use the top posts for winches, inverters, and other high-current add-ons. Don't throw away the plastic
terminal caps; save them in case you want to store the battery later. When bench-testing and charging a GM-style battery, don't
just run a bolt into the delicate side terminals. There are only a few threads inside and they can easily be stripped or burned due to
arcing, or the terminal slug can be loosened in the case when the bolt bottoms out. Instead, always use a washer and jam nut on
the bolt for a tight, secure connection. Also make sure to keep the terminals clean-corroded battery terminals produce more
unnecessary battery replacements (and a zillion other electrical problems) than any other single cause.
Here's all you need to do: Grab another car battery with a decent charge on it (12.4 volts or better) and
connect it in parallel to the problem battery using a set of jumper cables. Then activate the charger and
charge the battery normally, being careful to follow the manufacturer's instructions for current and
voltage limits. It's as simple as that. The second battery supplies the voltage that tricks the charger into
supplying the necessary current. After an hour or so, you can remove the second battery and continue
charging. We tried it and it works. No matter how deep the discharge we applied, we were able to bring
the battery back to a full state of charge using our cheap but trusty bulk charger.
You can now find chargers that are specifically marketed for AGM batteries. They're nice but by no
means necessary. However, some recent chargers have a switch position on their control panels marked
AGM/gel. Since AGM and gel batteries have rather different charging requirements, that position is
somewhat bogus, according to several AGM battery manufacturers. They recommend selecting the
conventional switch positions with these chargers.
Of course, you can avoid all these headaches with deep discharge and parasitic loads in the first place
simply by using a float charger. Also known as battery tenders, these units deliver a small (500 to 800
Milli-amperes) but constant charge to the battery, keeping it fresh and fully charged. Just connect the float
charger to a wall socket and to your battery when your car is not in use and you're good to go. We've seen
basic versions of these chargers on sale for as little as 10 bucks-which is the deal of the century,
especially when compared with the hundreds of bucks you'll pay to replace a dead AGM battery. As an
added bonus, you'll know that whenever you want to drive your rod, the battery will be ready and waiting.