Sure, everyone will tell you, you need more back-up systems than a
nuclear power plant, but here's a real world practical solution that
balances safety with cost and space considerations. I have a similar size
size boat with the same sort of electronics. I'm guessing from your boat
and equipment that you use your boat for day time outings mostly on
inland lakes or close to shore. I stick to the lakes. I got one of those
combo starting batteries; half starting battery, half deep cycle. It
works great and is going on four seasons. Nevertheless, I did want a
back-up. However, there really was no room or good place on my boat for a
second battery. Given where I boat, there was little danger of a dead
battery situation becoming life threatening. But still could be a major
headache. I bought one of those portable jump start batteries and stowed
it under a bow seat. They're like Frosted Flakes, they're greeeeeat! I
thought there might be a problem holding the charge over long periods,
but they don't even seem to lose their charge over a year or more (I top
it off every more than that just to make sure, but one time I forgot and
there still was a full charge.) I had to use it once because like a
dummy, I drained my regular battery. I thought there couldn't be much
kick in the relatively small battery, but the engine cranked as fast as
always and started right up. Best $50 I ever spent.

"ToneJohn" wrote in
:

Well I plan on only getting 1 battery. Again i have limited
electronics on board that will take alot of juice. So that being
said, should i get a starting battery (auto one) or a deep cycle group
31 battery.....


wrote in message
oups.com...
You can start with a deep-cycle battery, adequately rated, without
damaging the battery. You cannot deeply discharge a starting battery
and say the same.

It does matter if you get a deep cycle battery. It doesn't matter if
you get a "starting" duty battery, provided you ave the amperage to
do the job. (That should not be interpreted to read that you don't
need a dedicated battery for starting purposes).