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Need Battery Advice

Posted: Tue Jul 23, 2019 9:55 pm
by yaiboat
What are the best batteries for my small boat with a trolling motor?

Re: Need Battery Advice

Posted: Wed Jul 24, 2019 4:37 pm
by galamb
There is only a couple of "manufacturers" that build every battery on the market.

Clarios is the largest - (formerly Johnson Controls who bought out Delphi who used to be the biggest) and East Penn probably account for over 95% of every battery out there regardless of what brand is on the battery case.

So brand is not very important. What is, is matching the battery to your "needs" as in do you need a starting battery with deep cycle capabilities, a starting battery AND a deep cycle battery, and how much "deep cycle" power do you need.

Once you figure out those answers then you can choose between the three typical battery types - standard lead acid, absorbed glass mat (AGM) or spiral grid (those are in the $, $$, to $$$ order). In most cases a standard lead acid battery will last you about 3 seasons with typical use. The AGM gives you the option of mounting it sideways etc, "may" give you a touch longer life etc and the spiral grids have the best power storage (all else being equal) and tend to last longer - but despite costing twice as much as the lead acid, they don't last "twice as long or give you twice the power" in a similar sized/class of battery.

There is a number of "dual purpose" options for batteries that (claim) to be both "starting and deep cycle". While convenient if you can only carry one battery, they don't do "either" as well as an independant starting or deep cycle battery (the lead plates in the battery are quite different for the two types, and the attempt to get a plate that does "both" is not totally successful) - but if your space/weight/wallet size is limited and you need one battery to do it all, they are functional.

Marine batteries are mainly found in one of three "group sizes".

Group 24 is the smallest and will "typically" have the lowest cranking amps which is typically stated in cold cranking amps, CCA (or marine cranking amps, MCA, on marine batteries which rates the amps "higher" since boats are only used in the nice weather when a battery produces higher amps than in the cold) - they will also "store" the lowest number of amp hours AH of the battery classes.

Group 27 and Group 31's are larger with generally more MCA's and more AH's.

A group 24 might have an MCA rating of 625 and AH of 65 (although they will vary). The reserve capacity (which is also often listed) is of little value/concern on a marine battery.

With 65 "amp hours" that would allow you to run a 30 pound electric trolling motor at full tilt for just a hair over 2 hours (30 pound motor tends to draw 30 amp if it's run at max setting - so would "eat" 30 amps per hour depleting that GP24 batteries 65 stored amps in about 2 hours) - in reality it would give the typical user at least 8 hours of run time since most either have a (maximized) variable speed motor (which uses a pcm controller to drastically reduce actual used power) or if it's the older style 5 speed or whatever, you typically don't have it "cranked" and a 30 pound motor in (2nd) only draws about 8 amps (65/8 = a hair over 8 hours).

A group 27 might give you upwards of 90 amp hours and a group 34 will generally give you a little over 100 amp hours - but they do vary a little by brand and configuration (although they are probably made by one of two companies, the individual brands do sometimes have batteries made to their specifications - so some variance).

Re: Need Battery Advice

Posted: Fri Jul 26, 2019 11:34 am
by rleete
Nice write-up.

From my extensive research into batteries, I concur with what you wrote.

Re: Need Battery Advice

Posted: Sat Jul 27, 2019 6:49 am
by mrintense
Thanks for the useful advice Graham

Re: Need Battery Advice

Posted: Wed Oct 09, 2019 7:02 pm
by gpcramins
I used a group 27 marine battery (Walmart brand, probably the manufacturer specified in Graham's post) with a Minn Kota Endura MAX 55 in a 15' transom canoe with great success. I could run 8 to 10 hours no problem with reserve to spare. The boat hull weighed approximately 100 lbs with another 300 lbs of gear counting myself and dog.

One option to consider, you can bring a small generator and battery charger (what I did) to ensure a trip home should you run out of power. I just beached the boat, fired up the generator, and charged the battery while I fished. added no more than 45-50 lbs of weight...