From West Marine's West Advisor
While you'd
hardly think of specifying a particular chemistry for your car battery, it is
quite common for marine batteries because they are available in three different
chemistries that suit different applications. Most of our batteries fall into
one of three categories: flooded, gel, or AGM. Your choice should be based on
your needs (deep cycle vs. starting), the capacity and life span you're looking
for, and your budget.
All three
battery types depend on the chemical reaction of lead and sulfuric acid to store
and release electrical energy. Unlike the others, flooded batteries rely on a
reservoir of liquid sulfuric acid to act as a pathway between positive and
negative plates. These plates produce hydrogen and oxygen when charging but
unlike gel and
AGM batteries, which recombine the gases and re-introduce them to the
system, vented wet cell batteries allow the gases to escape into the atmosphere.
As a result, flooded deep-cycle batteries require periodic inspection and
topping-off with distilled water. Venting into the atmosphere increases the
level of hydrogen gas around the battery, which requires ventilation of battery
boxes and compartments. The venting occurs during charging and has a benefit.
Compared to to gel and AGM batteries, wet cell batteries are not sealed, (so
they can be topped-off) and they are better suited to accept overcharging.
Properly charged and maintained, our premium flooded deep-cycle batteries are
capable of a few hundred to more than a thousand cycles, which can translate to
many years of dependable service at an initial cost that's substantially less
than AGM or gel batteries with comparable amp hour ratings.
Gel
batteries (a.k.a. sealed, valve-regulated or SVR) are sealed and use pressure
release valves to keep their internal pressure at a slightly positive value, yet
they can release excessive pressure if needed. The impossibility of adding
water, or gaining access to the battery's inside, forces the manufacturer to
make an extremely high quality battery with great consistency. The "gel" is a
combination of sulfuric acid, fumed silica, pure water, and a phosphoric acid.
When initially mixed, the gel is quite liquid, and can be poured easily. The gel
is drawn into each cell under a vacuum up to six times, which eliminates voids
and pockets of air that can result in dead spots on plate surfaces and loss of
capacity and performance. Once it is in place, the gel becomes quite viscous,
making the battery impervious to leakage in case the battery gets inverted or
its case sustains damage. As in a flooded battery, charging causes a small
amount of hydrogen and oxygen to be generated at the plates which, due to the
pressure inside the cells, is combined to create water (so called "recombinant"
batteries). This keeps the battery from drying out due to charging, but it also
requires that the vessel's charging system be very carefully regulated to
prevent high voltage over-charging.
AGM
(Absorbed Glass Mat) batteries feature a dense separator compressed tightly
between the battery's positive and negative plates. These specially designed
plates are saturated with a precise amount of acid electrolyte, just enough to
activate the battery. During charging, the precision pressure valves allow the
oxygen produced on the positive plate to migrate to the negative plate and
recombine with the hydrogen, producing water. In addition to providing equal
saturation across the entire surface of the battery's positive and negative
plates, the fibers in the dense glass mats embed themselves into the surface of
the plates, like reinforcing rods in concrete. This provides more plate support
and better shock and vibration protection than in conventional batteries. The
high packing density results in lower internal resistance, allowing AGM
batteries greater starting power and greater charge acceptance than other types
of deep cycle batteries. Long life and outstanding performance make our SeaVolt
AGM batteries excellent dual-purpose batteries for boaters who require quick
starting power and reliable deep cycle ability.
We chose
East Penn as our primary battery vendor due to their superior technology and the
company's stellar reputation for making marine, telecommunications, industrial,
and automotive batteries. A low return rate and positive feedback from our
customers support this choice.
No matter what
kind of battery chemistry you choose, the following recommendations should help
you get the best performance
Stay with one
battery chemistry (flooded, gel, or AGM.) Each battery type requires specific
charging voltages. Mixing battery types can result in under or overcharging.
This may mean replacing all batteries on board at the same time.
Never mix old
batteries with new ones in the same bank. While it seems like this would
increase your overall capacity, old batteries tend to pull down the new ones to
their deteriorated level.
Regulate
charge voltages based on battery temperature and acceptance (manually or with
sensing) to maximize battery life and reduce charge time. Ensure that your
charging system is capable of delivering sufficient amperage to charge battery
banks efficiently. This generally means an alternator with 25% to 40% as many
amperes as the capacity of your entire battery bank.
Keep batteries
clean, cool and dry.
Check terminal
connectors regularly to avoid loss of conductivity.
Add distilled
water to flooded lead acid batteries when needed.
Clean
corrosion with a paste of baking soda and water.
| Battery Type | Pros | Cons |
| Wet Cell |
|
|
| Gel |
|
|
| AGM |
|
|