Cruising World – August 2019

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77

of the equipment needed to
properly charge these batter-
ies to ensure maximum cycle
life, and I think you’ll fi nd a
signifi cant jump in the gel-cell
cost per amp hour. Read on,
and I’ll explain.

GEL-CELL POTENTIAL
Battery technology has
improved considerably in the
past 20 years, in part because
of the interest in electric cars
and trucks, so a change in the
cost-per-amp-hour numbers
is to be expected. Even back
when I originally looked at
them, I remember talking
with the folks at East Penn
manufacturing, makers of the
popular Deka brand of marine
batteries. They told me their
warranty data indicated that
their gel-cell line of batteries
would outcycle fl ooded-cell
or AGM technology in
deep-cycle applications. Their
position remains the same
today.
But there’s more to consider
than just the number of cycles.
Because of their construction,
gel-cell batteries are the most
fi nicky about their recharge
regimen, and in my own
experience, improper charging
is what kills them—and it
can happen rather quickly,
typically in one sailing season
or less. So, if you want to go
the gel-cell route, be prepared
to upgrade your engine’s alter-
nator to one with a remote,
programmable voltage regula-
tor. Also, make sure that your
shore-power charger, if you
have one, has a gel-cell setting
or adjustable voltage levels for
its various phases of charging.
Any solar- or wind-charging
units must be run through a
charge controller that can han-
dle the lower voltages required
by the gel batteries.
Here’s why: Depending
on the manufacturer
requirements, gel batteries
should never be subjected to a
recharge voltage greater than
14.7 volts, and some vendors
state no more than 14.1 volts
for any sustained period.
Therein lies the problem:
Internal voltage regulators on
engine-driven alternators are
of the constant-rate variety

and typically produce in excess

of 15 volts. So, in a nutshell,

whenever your engine is run-

ning, you are rapidly destroy-

ing a gel-cell battery unless a

programmable regulator has

been installed in the system

and set appropriately.

Now, don’t get me

wrong—gel-cell batteries have

some real advantages. They

are sealed-valve-regulated,

meaning they will vent, but

only under overcharging if ex-

cess pressure builds up. They

require essentially zero main-

tenance, and have excellent

deep-cycling capability and a

very low self-discharge rate (3

percent per month). But again,

they must be connected to a

properly calibrated charging

source. If your boat is already

equipped with gear that can

be adjusted to meet the need,

this could be a great choice.

Otherwise, some detailed cost

analysis is needed, and you

might fi nd that your cost-per-

amp-hour is too high after all

the upgrades are factored in.

A LOOK AT AGM

AGM batteries have come a

long way over the past two de-

cades as well. Spiral cells and

thin plate pure lead (TPPL)

are two of several examples

of how battery-makers have

worked to optimize the

amount of power they can

squeeze into a battery of a

given size. Like their gel-cell

brothers, AGM batteries

are sealed-valve-regulated,

low maintenance, and can

be discharged to extreme

levels—80 percent of their

capacity versus 50 percent

for conventional fl ooded-cell

batteries. AGMs also have a

signifi cantly higher recharge

acceptance rate—35 to 45

percent of capacity in amperes

versus 25 to 30 percent for

traditional fl ooded-cell batter-

ies. And they have a very low

self-discharge rate, similar to

gel cells.

Unfortunately, like their

fl ooded brethren, AGM

batteries are prone to sulfation

when left in a partially charged

state for extended periods of

time. Sulfation is a natural

occurrence that over time

will coast the cell plates with

nonconductive lead-sulfate

crystals. This effectively

reduces the plate’s exposed

surface area to electrolytes in

the cell, and in turn reduces

the capacity of the battery,

ultimately rendering it useless.

This is a common

cruising-boat issue that a

conscientious captain can

easily overcome with a little

bit of diligence. The fi x here

is to make sure these batteries

frequently get a full charge.

The good news is that

unlike gel cells, AGM batteries

can take regular and higher

ampere and voltage amounts

when recharging, with min-

imal fear of damage. In fact,

one potential problem is that

the alternator will be working

so hard, it might overheat and

be damaged. In the case of a

shore-power-supplied charger,

just make sure its capacity

rating is adequate so it’s not

running at 100 percent output

constantly. If the charger was

marginal when used with

fl ooded-cell batteries, replac-

ing old batteries with AGM

technology could force the

need for a new charger, again

skewing that cost-per-amp-

hour number.

Another thing to consider,

if you’re replacing traditional

batteries with AGMs, is

their size and shape. Because

of the way in which these

batteries are made, they do

Battery technology has evolved alongside the power

appetites of modern sailboats such as the systems-rich

Amel 64 (opposite). Manufacturers are packing a lot of

electrical punch into AGM batteries, which are available in

a wide range of shapes and sizes (above, top).