Chuck,

I might have been sold a bill of goods (this wouldn't be the first time),
but I was told by boat/us that the Marine Dual Purpose Battery would have
the extra "cranking amps" for a longer period of time, than a Deep Cycle
Battery would provide. I have twin 5.7 gas engines, which require high
cranking amps.

According to this rep. (who seemed to know what he was talking about) , the
Dual Purpose Battery does take more abuse than an exclusive Starting Battery
will, but will not provide the cranking amps for as long of a period as the
Starting Battery or Dual Purpose Battery, (but they do make marine starter
batteries that are supposed to be heavier than the average starting
battery).

So is it your opinion that I was sold a bill of goods?


wrote in message
ups.com...

wrote:
I am reading a book called "Powerboater's Guide to Electronic Systems".
The book recommends using two dual-purpose batteries if the boat is a
center console. A dual purpose battery is supposed to be good for both
cranking the motor and serving as a house battery. I am wondering why
a dual purpose battery is the best kind for a center console, but not
the best for a cruising boat (he recommended a combination of a
starting battery and a deep cycle battery for a cruising boat). What
are the reasoning behind this? Won't a combination of a starting
battery and a separated deep cycle battery is just as good for a center
console?

My center console is having two dual-purpose batteries just like what
the book has recommended. I guess this is good. I just don't know why
this is good.

Thanks in advance for any info.

Jay Chan


Sounds like the "Powerboater's Guide to Electronic Systems" wasn't
written by a powerboater.

You've got some bad advice.

There is almost no earthly reason to ever have a "starting battery" on
a boat, except it will help the battery manufacturer sell a greater
number of batteries each year. Starting batteries have lighter weight
(thinner) plates so additional surface area can be exposed to the
electrolyte and maximize the CCA rating in a given case size. Those
thin plates disintegrate faster than the thicker plates in a "deep
cycle" battery, and when one plate is gone the battery is toast. The
thin plates make it bad practice to discharge a starting battery very
deeply- the recharge stresses the thin plates and leads to premature
battery failure.

(I use Rolls batteries on my boat. They are sold with a 10-year
warranty. Rolls doesn't even offer a "starting battery", and the
Rolls/Surette company is one of the premiere manufacturers of flooded
cell batteries.)

If space is so tight that you just can't possibly fit a deep cycle
battery rated for sufficient CCA, then I suppose a "starting" battery
must be used- but that situation will arise once in a couple of hundred
installations. In fact, if space is *that* tight, you battery
compartment is probably inadequately ventilated and you have some
other, potentially more serious problems.

Best plan: Always use a deep cycle battery for house loads. Use a deep
cycle battery with sufficient CCA to start your engine in nearly all
applications. Have at least two batteries, properly cabled and
switched.