Kevin -
Just do what the rest of us do - buy a Guest!
Their products and customer service are second to none!
For a weekend fisherman, 5 amps per trolling motor battery is sufficient plus a connection for your cranking battery. (Your big motor has a charging system built in for the cranking battery.)
I see that you've got a Nitro 180/150 Merc! I had a 180 with a 115 Merc - wish I had had your motor!
If you've got just one trolling battery, the Guest 2611 should do the trick nicely; if you've got two trolling batteries, go for the Guest 2613.
me!
P.S.
They have a banner that regularly appears at the top of the page. Click on it and you'll be taken to their website.