what size battery?

[dubnvento]

I'm unsure what size battery I need for my boat so here's the low down. It's a 15ft Gregor with a tiller operated 18HP fastwin. The battery would need to power a 30 lbs thrust trolling motor for a minium of 8 hours at half thrust as well as auxiliary lights for a 15 minute period in the morning before light. I saw a post on her that talked about amps and how long they power a trolling motor at full draw but I still was left with questions. At my local marine dealer they had a 105 minutes @ 25 amps I believe, a 70 minutes @ 25 amps and a 50 minute @ 25 amps batteries all made by Trojan deep cycle. Any thoughts?

 

[tashasdaddy]

Re: what size battery?

pass on the trojan, the last one i bought, had to be replaced 5 times under warranty. i would get a group 31 deep cycle battery, it is heavy, but will last and hold the charge, if you go to LED lights they use almost no power, i have them for my courtsey lights, and at all fishing stations, so i can bait a hook at night.

 

[Wee Hooker]

Re: what size battery?

Does your outboard have an altinator?
Are you looking for 8 solid running hrs @ 1/2 power/14amps or intermitant power for a 8 hr trip?

 

[sschefer]

Re: what size battery?

If you knew how much current your motor draws at 1/2 thrust you could just do the math. Do you have the manual?

 

[Silvertip]

Re: what size battery?

The difference in price between these batteries is not significant. So why not just buy the biggest (largest capacity -- as in reserve minutes) you have room for. A 30# thrust MinnKota Edge draws 30 amps under maximum load. So in your example, the 105 min reserve capacity would run your motor wide open for a little under two hours. Forget the 70 and 50 minute reserve capacities as they are not suitable. You should check your local farm store. I buy my deep cycles (group 27) there and I believe the one I have on my pontoon is 150 minute and was $69.00. This battery runs my 55# Minnkota PowerDrive V2 all day (obviously not at wide open throttle settings). It is used intermittently for position fishing and very slow trolling. You do not need to spend big bucks on batteries if they are properly maintained with a quality smart charger. Always fully charge a deep cycle immediately after use. An even if your motor has an alternator, it will not have the capacity to keep that battery topped off.

 

[fishrdan]

Re: what size battery?

I have a 14' jon boat with a 40# trolling motor and 2 group 31 batteries. After 6 hours of constant trolling on speed 2 and 3, with the occasional burst to speed 4 and 5 they are ready to be charged. These batteries are 2 years old so I guess they probable performed better when new.

The lights really don't use much power compared to the trolling motor and since you are only going to use them for 15 minutes I wouldn't factor them in.

I really doubt you are going to get 8 hours of trolling on 1 battery, even pushing it on 2 batteries. It's really tough to guess how much power you are going to use, just yourself in the boat or 2 other BIG buddies, wind, current, etc... I'd get the biggest deep cycle battery you can (group 31) and see how one does (carrying a backup battery if you have one) then gauge it from there. If you buy a group 24 battery and it only runs the trolling motor for 3 hours you are not even 1/2 way to your goal.

My buddy has a 12' lund with a small Minnkota trolling motor and 3 group 24 (or 27???) batteries, I think he gets about 8 hours of constant trolling with his setup.

Remember when you add batteries to a tinny you should place them forward for good weight distribution, keep them at the stern and the boat will be stern heavy. Just balances the boat out better, makes it ride better and improves hole shot/getting on plane.

 

[Silvertip]

Re: what size battery?

The issue with these smaller troller motors and even the bigger units that don't have the maximizer circuitry is that they consume nearly the same amount of power at slower speeds than faster. This is because the older units used speed coils (wire wound resistors) so the shunted voltage was simply turned to heat. The controllers in newer units although better are still nowhere near as efficient as the maximizers (MinnKota-speak). MotorGuide uses similar technology. In slow trolling applications, you would be money ahead by buying a 40 pound thrust MinnKota PD or equivalent MotorGuide and running at very slow speeds. You could certainly fish at least most of the day on one battery. I do that with a 55# PD on my pontoon -- but at a combination of holding/position fishing or intermittent slow troll/drifting.

 

[dubnvento]

Re: what size battery?

I ended up buying a 24 group Trojan 100 min @ 25 amp deep cycle battery. This is the only brand the retailer I bought it at had and sense I had gift cards from the holiday, it made it easier to purchase. Hope this works for my application. And to answer previous questions. I don't use a trolling motor constantly. I use mostly on small lakes to get out to my spot then shut it off and maybe use it intermittently to move once and awhile or to troll for a short time.