I know some of you already know this, this is to help the OP and other new folks in the future....
Trojan's are the "Cadillac" of batteries. You could chose a less expensive brand of golf-cart battery and still come out ahead when compared to an ordinary Marine battery.
Bill, all that salesman knows is the training he received for "application". Trojan also makes batteries for floor buffers, that doesn't mean that it's improper to use them in another application.
Here's the deal:
Voltage= "pressure" or "potential"
Amperage= "flow" or "capacity", or you can think of it as a tank of stored energy like a fuel tank
. The more amps you have, the bigger your "tank". Also, when measuring amps in an active electrical
circuit, you're measuring the "flow" of "electrical water" (electrons) as they pass from the negative battery plate, through the "load" (lights, electronics
, etc) and to the postive battery plate. When you charge the battery, you push the electrons back to the negative battery plate.
6v and 8v golf cart batteries have the same amount of lead and active material on the cell plates as a similar size/weight 12v battery. The difference is, the plates are thicker and fewer, so although the voltage is less, the capacity is greater because the single
plates have more surface area. By connecting (identical) batteries in "series" (+ to -), you double the voltage, while your capacity remains as if you only had one of those batteries. If you connect them in "parallel" (+ to + and - to -) then you double the capacity but the voltage remains as if you only had one of those batteries.
You need 12 or 13v of "pressure" on your electrical
circuits for your lights and gear
to function correctly. You're seeking to buy the biggest capacity or "energy tank" you can afford, and that will fit in your boat.
So you have a choice:
a) You can wire two 12v Marine batteries in parallel
for 12v @ double the capacity of one of those Marine batteries.
b) You can wire two 6v golf cart batteries in series
for 12v @ the capacity of ONE golf cart battery (which is certainly more than a single
Marine battery, but might not be more than 2 of them in parallel
Simply look at the amp capacity of the batteries you're considering, do the math, compare the prices and see which configuration will give you the capacity you desire for the best price
Whatever you do, make sure that you buy 2 new, identical batteries, manufactured roughly at the same time. Otherwise you'll find yourself with batteries that are out of balance, one will discharge into the other, and they'll kind of kill each other in a short time.
I converted a 1974 VW Bug to 100% battery-electric drive. It had a range of 40 miles and a max speed of 70 mph and I put 10,000 miles on it before I sold it. I had SIXTEEN 8v golf cart batteries to balance, for 128volts, nominal. Wiring
up 2 batteries is cake.
Hope this helps!