gradyfish22 said:
>snip
...do not use a deep cycle, the starting will signifcantly wear down the plates and kill the batteries life quickly.
>snip
Come on guys, this is just not true. I find this kind of erroneous information frustrating on a forum that serves to help fellow owners.
A deep cyle battery is very well suited for our boats when they run a lot of equipment like radios, pumps, lights, sounders, etc. As long as the deep cycle is sufficiently sized to handle the starting needs they work very well and will last the longest. And they don't 'wear down the plates', that's just not true.
A starting or 'dual-purpose' do not do well with deep discharges as they have thinner plates than a deep cycle. Nor does any battery last a long time if they are left partially discharged for any length of time. The deeper they are discharged and the more times they are discharged, the shorter their life - this is true for any battery type, but espcially for starting or light duty types.
A deepcyle (or bank) with a cranking battery (or bank, or one for each engine) in reserve is the best solution. But you need the second charging circuit to maintain the cranking battery you have in position 2. This way if you run down your main battery to where it won't start your motor, you can switch to your fresh cranking battery. A deep cyle will way outlast the others with this type of configuration.
If you are running a multi-engine, mulit-battery setup, then you can usually configure a starting and house battery setup. Golf cart (6v) can be very useful in this type of application, outlasting 12v batts by a long margin, and providing a ton of reserve power. Very popular in the RV's, not as much in boats.
While AGM's have several advantages to flooded cell lead-acid types, they are considerably more expensive and can require special charging protocols. For me, the lead-acid are a cheap solution, easy to maintain, and their condition can be easily monitored. Costco, Sams, Walmart, are good sources with cheap prices and fresh inventory. Guys with big bucks to spend can gain some longer life with the AGM's, and are espcially well suited where they have limited access or where acid spillage would be a problem since they can be mounted in odd configurations.
Good battery info here:
http://www.windsun.com/Batteries/Battery_FAQ.htm