Left: AGM batteries have expanded the options for cruisers, with faster recharge times, higher terminal voltages, and lower
maintenance. Right: While they remain popular, flooded batteries cannot be recharged as quickly as their AGM and gel cousins.
of both power and sailing vessel applications and
I believe it’s safe to say the jury is in; they do have
much to offer.
Invented in the mid 19th century, in their present
form conventional flooded batteries (they have sloshing,
liquid sulfuric acid inside) have remained essentially
unchanged for decades. While they’ve been tweaked
and improved along the way, the technology is mature.
High-quality flooded batteries are rugged, long lived,
and generally perform well, some lasting for more
than a decade, however, their shortcomings are well
known to those who have used them. Their primary
weakness is that they are slow to charge. Typically,
their maximum charge rate is no more than 25 percent
of their amp hour capacity. That means a flooded
400-amp-hour battery bank could only accept, initially,
100 amps of charge. Because the resistance in a battery
increases as it charges, that charge rate tapers off rather
quickly, which means it could take three or four hours
to replace 200 amps from this bank. Additionally,
because the charge process creates heat and gassing,
flooded batteries lose some of their water content with
each charge. Eventually this water needs to be replaced.
Forget to do this and you’ll quickly and prematurely kill
an otherwise good battery. As flooded batteries charge
they also emit acid vapor. You’ve probably seen this
accumulate on battery tops, it doesn’t readily evaporate.
I know I’ve encountered it many times because of the
number of trousers and coveralls I’ve ruined as a result.
Flooded batteries have one more trick up their sleeve,
as they charge they produce explosive hydrogen gas,
which has to be safely vented out of a battery box or
Nearly all flooded battery maladies are negated by
switching to an SVRLA. The charge acceptance rate
of SVRLA batteries is likely their greatest attribute.
They are capable of accepting up to 50 percent of amp
hour capacity for gels and 100 percent or more for
AGMs, which significantly reduces the time it takes
to recharge battery banks. SVRLA battery cases are
sealed and slightly pressurized, which means that if
properly charged, they won’t emit hydrogen gas or acid
vapor and they never require the addition of water. If
overcharged, however, they will produce hydrogen,
so they still require ventilation. The electrolyte in gel
batteries is immobilized as a gel, hence the name, by
mixing it with very fine silica, while AGM electrolyte
is immobilized in a glass fabric, making SVRLAs
Steve owns and operates Steve D’ Antonio Marine
Consulting ( www.stevedmarine.com), providing consulting
services to boat buyers, owners, and the marine industry.