Trolling motor issues/question

I just finished building my 1st boat (a small 8' pram), and was given an old Minn Kota trolling motor that my father was given (used) after he got back from the Vietnam War. He believes it to be about 30 lbs. of thrust. He also lent me a group 29 deep cycle marine battery that he had used for camping for several years. It had a decent charge, but I still charged it up to about 13.3 and brought the boat out on a tiny lake on a calm day. It barely moved. I know trolling motors are supposed to be slow, but I could not get across the lake without paddling. Floating leaves were moving past me - literally. I assumed the battery was weak, but when I got home I checked and it was still at about 12.6. I figured his 40 + year old motor was the problem.

The next day I went to Walmart and bought a Minn Kota C2 Endura 40 lb. trolling motor. I went out to the same lake and had the same results (even though I had recharged the battery). I actually tilted the trolling motor up to see the prop out of water, and in speed 1 it was rotating about 15 RPM. 15 isn't a typo. I could have stopped it with my finger.My boat is no racer, and I'm a big guy (about 230 lbs.), but its draft is only about 4" and the bow transom was well clear of the water. When I checked the charge, it was a bit over 11. It had run on speeds from 1 to 5 for about an hour.

My question (sorry this is so long), is...can a battery that gives good readings still not power a trolling motor correctly?

 

Have you had it tested by an auto parts store?

 

Looks like you need a new battery. If it is several years old,it won't take a charge any more.

 

The voltage when not under load is not a good indicator of the condition of the battery.

 

Take your battery to a local golf cart shop.

They will have the $500+ battery tester that will give a reading of the batt condition,

 

Thank you all for the good advice. I did not know that a battery not under load will often read differently. I tested, and it was not holding a full charge, so I bought a new group 29. Now I just need the New England weather to cooperate so I can test it out.

 

A 12 VDC car or deep cycle battery will read 12.6 (or higher), on a full charge and no load. Each cell is 2.1 volts. You really need to load test the battery to find it's real condition, but to save this bother, I can tell you, the battery is spent, get a new one.

It sounds like you're powering up a small pram like boat. It's not going to be fast, especially given the load (no offence intended) so range will be weak too. Expect the 3 MPH range, as the little motor is doing precisely what it's designed to do, run at trolling speeds. You can increase this speed (a little) with prop changes, but you'll also lose some range.

 

a trolling motor will bloody your fingers at 1st speed setting if your battery is any good at all.