Evgenij Barsukov wrote:
I am looking to buy a deep-cycle battery to run a 55 lb trolling
motor (45A max/12V) which will be used as the only motor for an
inflatable boat for fishing.

By far the most bang for the buck is golf cart batteries. Looking at the
cost per 12V amp-hour, they are about 2/3 the cost of car batteries and
1/2 the cost of marine batteries. Of course, they are 6V so you have the
trouble of wiring them in series, but that isn't difficult.

For our boat, I bought a pair of Exide Gr 31 dual purpose batteries from
Agri-Supply
http://www.agri-supply.com/catmain/1200005.htm
I don't know what the reserve rating is but their amp-hours are about
115 so one of those would certainly drive your motor at full power for 1
hour, and the cost is about $65

Remember that the power extracted from the battery follows a curve, so
that if you have 1 hour at full throttle, you have more than 2 hours at
half throttle and possibly 6 hours at 1/4 throttle etc etc.

Hope this helps

Doug King