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Knots to Know
Charging Your Boat
Marine batteries, no matter the type, respond to
charging in different ways, and using the right battery charger in
the proper way will help preserve the life of your boat's batteries...
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Trailering and Tires
Getting Ready for Winter
Usually, by the end of October, many of the lakes have “turned over” for the
winter. Morning steam rising from the water indicates that the heat energy
stored in the lake from the long hours of summer daylight is beginning to
return once again to the atmosphere as the water begins its annual slumber
and ultimate renewal. There is perhaps still a little time left for one
final outing, but most – if not all – of you have taken your boats out of
the water and gotten them cleaned out, “winterized” and ready for next
spring’s trek back to your favorite fishing spots. You take very good
care of your boats, motors, poles, reels and other gear inside the boat.
But have you really taken the time to look after one of the most important
pieces of equipment that you have on board – your batteries?
Most of us take our boat batteries for granted, in much the same manner as we do our
car batteries. I used to do that. In fact, I had a car that sat in the
warmth of the garage all winter. I thought that an occasional blast from
a charger would be enough to do the trick. Boy, was I wrong. And the
result was a new battery about every other year – until, after a lecture
from my mechanic, I got a little bit smarter about batteries.
A battery can lose – depending on how and where it is
stored – up to 30% of its charge per month – just sitting around the
house or garage! And there are all kinds of things that affect battery
charge and loss thereof (like temperature, humidity, state of discharge,
age of battery, etc). Most of us never consider any of them.
Not unlike young children, battieries require loving
care: call it maintenance. Getting the right battery for the
intended task is only part of the story – keeping that battery healthy
with the proper charging and maintenance will ultimately ensure that you
will have the necessary power when you call for it!
Which type of battery you choose is based on your needs
(deep cycle vs. starting), the capacity and lifespan you are looking for
and your budget requirements. Although I have found that the subject of batteries and battery maintenance
to be a multi-faceted
subject that encompasses many different topics, I am going to limit my
discussion to a few of the most important “basics”. I want to briefly
There are two basic types of 12-volt
- Cranking -- or starting
-- batteries: These are designed specifically to start your
main engine. They are made with thinner and more numerous lead
plates inside, allowing for more surface area and thereby providing
the quick and massive amounts of energy required for tough starting
jobs. While the motor is running, the alternator inside will
easily and quickly replenish the used energy. If your boat is
powered by a newer model outboard with sophisticated computers,
pumps and sensors, you definitely want to make certain you have
enough starting power. It's a good idea to check your owner's manual
for the recommended MCA (Marine Cranking Amps: a measurement of the
number of amps a battery can deliver at 0 ° F for 30 seconds and not
drop below 7.2 volts) rating before shopping for a battery; always
choose one with a rating equal to or greater than the recommended
- Deep-cycle batteries: These are
designed to power on-board electrical accessories such as trolling
motors, fish-finders, GPS, radios and the like. In general,
these batteries use energy at a much slower rate and often don't get
re-charged until the end of the day. This deeper and more
strenuous discharge is hard on a battery and requires a different
design type; the result is a battery with fewer but much thicker
lead plates that will withstand the deep cycling. Deep-cycle
batteries can withstand the rigors of several hundred
discharge/recharge cycles, while cranking batteries cannot.
It's important to understand that, because of their
design differences, substituting one battery type for another is not a
good idea. Use a cranking battery to power a trolling motor will
cause the battery to overheat and fail. Besides leaving you
without power in a moment of need, purchasing a new battery will
definitely be in your future. Substituting a deep-cycle battery
for a cranking battery will likely not provide the power needed to start
your outboard, possibly leaving you stranded a long way from your dock.
As it turns out, the design strengths of each battery type also are
their weaknesses in opposite applications.
Having said that, dual-purpose batteries that can perform
both these functions -- to some extent -- also are available. Keep
in mind however, they will not supply the same starting power as a true
cranking battery, nor will they provide the same number of
discharge/recharge cycles as a dedicated deep-cycle battery.
As if all that doesn't make things difficult enough, batteries
can be further described according to the configuration of the
electrolyte inside the battery... leading us to four categories that
all have their own advantages and disadvantages.
- Wet-Cell or Flooded-Cell Batteries:
Generally the most popular and the type most all of us are familiar
with, they have a number of cells inside that contain a liquid
mixture of sulfuric acid and distilled water. They have the
advantages of a somewhat lesser price, a high number of
discharge/recharge cycles (if properly maintained and taken care
of), are less likely to be damaged by overcharging and are a bit
lighter in weight than comparable AGM or Gel batteries. The
disadvantages are that most have vented, interior-accessible
designs, requiring regular inspection and making certain the cells
are topped off with distilled water. Venting also releases hydrogen
gas, meaning the battery compartment must be well ventilated. Other
drawbacks include possible spilling of corrosive battery acid, a
higher rate of self-discharge (6% to 7% per month) and the fact that
wet-cell batteries are more fragile in high-vibration environments
such as boats.
- AGM Batteries: AGM is short
for Absorbed Glass Mat, and these batteries feature a dense filling
of very fine absorbent fiberglass matting that is saturated with
acid/electrolyte and packed tightly between the battery's plates.
The design allows oxygen to recombine with hydrogen gas, thus
replenishing the battery's water content and alleviating the need
for refilling. Advantages include being truly maintenance free
(except for external cleaning). They are sealed (which doesn't
allow for gases or acid to leak), can be installed at any angle, are
shock and vibration resistant, have a relatively low self-discharge
rate -- ~ 3% per month) and can even withstand being immersed in
water (I guess that's in the event your boat gets swamped?).
The biggest disadvantages are that AGM batteries are more expensive,
are heavier and are quite sensitive to charging currents and
voltages; they are somewhat easy to overcharge, which can ultimately
ruin the battery.
- Gel Batteries: Gel
batteries too, are much like wet-cell batteries in that they are
filled with liquid electrolyte. The difference is that the
electrolyte is gelled with silicates before the battery is sealed.
Like AGM batteries, they use the special technology that eliminates
the need for adding water. Advantages? They are maintenance
free, sealed, low-temperature tolerant, shock/vibration resistant
and have long cycle life. Their most notable advantage is resistance
to over-discharge that can damage other battery types. Gels
have an internal self-discharge rate less than 1 percent per month,
so they can be stored for long periods without being recharged. And
because they aren't prone to develop life-shortening plate sulfation
when left uncharged, they are a good choice for boaters who often
forget to recharge batteries promptly after use. The bad news
is that these batteries are often almost twice as expensive as
comparable flooded-cell batteries and are also fickle about
charging; they require special chargers.
- Lithium-ion Batteries:
Lithium-ion batteries are among the emerging “super battery”
technologies. They have a high energy density and are
excellent for deep cycle applications. Compared to flooded
batteries, lithium batteries deliver a savings of up to 70 percent
in volume and weight and can offer three times as many charging
cycles. They handle incredible amounts of current and therefore can
be recharged faster than any other type. Currently in use
onboard high-performance offshore racing sailboats and others whose
owners demand extreme weight savings and cutting-edge performance,
Lithium-ion may be the future... Be prepared and willing to
pay premium prices.
Things that will
destroy a battery
There are essentially
two things that will quickly and easily destroy your battery: either 1)
undercharging it or 2) overcharging it. The majority of both deep cycle and
starting batteries are simply containers for a number of lead-plates, filled with sulfuric acid.
Undercharging them will ultimately cause lead sulfate to accumulate on the
plates; this will eventually destroy the battery because the normal
chemical reaction will be unable to continue. Overcharging the battery
will accelerate the natural corrosion of the plates due to excess
electrons being literally boiled out of the electrolyte. Ultimately, the
fluid boils away and the plates are exposed to the air, which ruins them.
SulfationHave you ever had a
battery that seems to work well but “dies” much more quickly than
expected? The problem may be a battery that is heavily sulfated
– often the result of only light use (being discharged by only 15% or
so). The sulfuric acid has become concentrated on the battery’s bottom
and sulfate crystals have begun to form. And even though a multi-meter
will indicate that all is well in terms of voltage, the capacity of
the battery has become severely reduced. Sure, the battery will work just
fine, but it will die much sooner than normal. There are certain chargers
that have a setting that will temporarily boost the charging voltage for a
brief period of time, causing a mixing of the electrolyte, and dissolving
the crystals. The process is called equalization and can be done –
depending on the manufacturer – about once a year. But beware: this
should only be done on wet cell batteries; this same process can ruin
other types. And you will need to make sure that you disconnect the
batteries from the electrical system to prevent the higher voltage from
damaging other equipment.
MaintenanceBatteries have come a long way since the 60’s. Back then, most – if not all – wet cell
batteries were dry to start with. In the storeroom of the gas station at
which I worked, there was a large box with a plastic bag filled with
electrolyte – sulfuric acid. I found out it was acid the hard way; in
filling a battery, I once managed to splash the electrolyte all over my
pants. I didn’t realize the power of the stuff until my work pants got
washed. They looked as if I had been shot by a machine gun: one leg
was nothing but holes! Now there is an incredible variety of
batteries that are available for every imaginable use: marine starting &
trolling, auto, agricultural, industrial). They all have at least
one thing in common: they need to be maintained to some degree – even
the “maintenance free” types. They will lose their electrolyte
during normal use and need to be checked; all need to be recharged.
Most of us still use the wet cell types for marine applications,
although there are essentially three distinct types of lead acid
batteries (see "Categories" above)
manufactured for marine applications, and any one type can be designed
and built for either starting or deep cycle applications. As I
mentioned, the gelled acid and AGM
types are essentially maintenance free since they are sealed. But because
of this, be very careful when recharging them; "smart charger" technology
is required or damage can easily result. They are also more
expensive but do have their advantages. The most important thing for the
flooded acid variety is to keep them full. Top them off with distilled
water only whenever possible, as minerals in tap water can contaminate the
electrolyte. Keep the terminal clamps clean and free of corrosion; coat
them with anti-corrosion spray or even petroleum jelly. Check connections
and keep them tight; watch for frayed wires and replace them. And for a
few bucks spent at your local auto parts store, a
Battery Hydrometer – used to
check the specific gravity (concentration of acid) is a good investment.
It is a great way to determine if one of the cells is bad. If the
difference in specific gravity is 30 points or more… it’s time to replace
Checkup and StorageWhether or not your boat
is stored for the season in a warm garage or out in the cold, your best
bet is to remove all batteries and bring them inside. A fully charged
battery with a perfect electrolyte level can probably withstand
temperatures down to zero degrees without freezing. But the colder it
gets, the more easily a battery can discharge, and therefore the more
easily it can then freeze at higher temps. If even one of the cells freezes,
the battery is shot! Fully charge them about once a month over the winter
and they will be ready when you are in the spring. Try to keep them off
of concrete floors if possible and cover the terminals to help prevent
discharge. The last thing you want is a dead battery on the launch ramp
on opening day, or a dead trolling motor battery.
No matter what kind of battery chemistry you choose,
follow these recommendations to get the best performance and longest
life from your batteries:
- Stay with one battery chemistry (flooded, gel or AGM). Each battery type
requires specific charging voltages and currents. Mixing battery types can result in
under- or over-charging, which may mean replacing all batteries on board
at the same time.
- Never mix old batteries with new ones in the same bank.
Old batteries tend to
pull down the new ones to their deteriorated level.
- Regulate charge voltages based on battery temperature and acceptance
(either manually or with smart-sensing devices) to maximize battery life and reduce charge
time. Ensure that your charging system is capable of delivering
sufficient amperage to charge the battery banks efficiently.
- Keep batteries clean, cool and dry.
- Check terminal connectors regularly to avoid loss of conductivity.
- Check fluid levels and add distilled water to flooded lead acid batteries when needed. Keep
batteries charged; leaving them in a discharged state for any length of time
will damage them and lower their capacity; it also reduces lifetime.
- Clean corrosion with a paste of baking soda and water.
With summer now officially here, I hope that most of you have either fished the opener
somewhere or are, like me, chomping at the bit to head to the lakes once
again. Make sure to check your batteries before you head
out. And when next October rolls around, you will perhaps remember a few
things from this article and make sure to take proper care of those very
important pieces of equipment: your batteries. For information on
charging and chargers, see my article on
Charging Your Boat Batteries.
On the Lake!
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Note: Due to the amount of traffic on this page and the
number of e-mails on boat batteries, I've decided to post some of
the questions and answers on a
page. I hope you find this
R. Karl recommends and uses the
Dual Pro Professional Series 2-Bank Charger, 15-amp