INEXPENSIVE Trolling Battery System
 

Hi! A former student has made an electric trolling motor contribution to my son's first boat project, but I'll need a battery/charger. Would I use a 12v trickle, regular car battery charger, etc.? Is a solar charger reasonable $? And what type battery would I be looking for?

Thanks!

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Look for a deep cycle marine battery with a high amp hour rating. As far as a charger goes, look for a smart charger that will both charge and maintain whatever type of battery you end up with (AGM, Lead Acid, etc). They are relatively cheap on Amazon.

Dan

Any deep cycle battery can be used. Any 12v charger will work but get one that charges then “floats” so it won’t overcharge. (I think today’s chargers all have this protection) a good investment would be a “Battery Tender” if you want to keep the battery charged and ready for action, and it will maintain your battery over the winter.
I have used the Schumacher brand charger for years with good luck but there may be more or better brands out there. I use a solar Battery Tender for my UTV and it works great. I have the solar panel on my shed and it maintains the battery year round. The BT brand is a bit more but there are Chinese ones on Amazon that will do the job.

Lol...while I was typing so were others...

Like this? https://www.oreillyauto.com/detail/b...y/24ms/4742399

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And this charger? https://www.amazon.com/DieHard-71219.../dp/B077742Y1H

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That charger looks good.
As for the battery, just get any “deep cycle”
Not sure if the one from Oreilly is a deep cycle or a high cranking start battery.

Great. That would work with pretty much any better I got for this, right?

Thoughts on the battery I linked above?

The person giving it to me said he used to use an old car battery, so I don't think it's very powerful.

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Any 12v battery, car, marine or otherwise will make the electric motor run.
It’s the repeated charging and discharging that a deep cycle battery will handle better than a cranking battery.

Not totally true Hill...some / many battery chargers only charge lead acid batteries. You don’t want to use a high amp lead acid charger on an AGM battery as you will destroy it. AGM need slow low amperage charging. Most smart chargers have selector switches for the type of battery being charged.

Dan

While any 12 V battery will work, I would look for one with a higher amp hour rating if it were me and make sure it’s a deep cycle battery made for charging / discharging. Like this one....

https://www.batteriesplus.com/produc...iABEgJX7_D_BwE


Dan

Ok, I think I might just hit up Batteries+. This is $80 after discount, and it looks like I can find a charger there within a few dollars of Amazon's.

https://www.batteriesplus.com/produc...ultra/sli24mdc

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Confirm this charger has built in internal battery type selector so you can charge lead acid, AGM, gel, etc.

Dan

That was what I just posted! Perfect!
And I'll confirm it works with AGM as well.

Y'all are the best!

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The one I posted is 105 AH battery...the one you posted is 75 AH...

Just thought you should know...

Dan

Oops, yup--a little too rich right now, though. I'm thinking the 75 would be sufficient for the size of the boat/motor?

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Size of boat or motor makes no difference, 12 volt is 12 volt. The 105 AH will simply last longer per charge....about 25% longer than the one you selected...

Dan

But doesn't the draw change with size?

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The larger the motor the larger the draw yes, but all things being equal the 105 AH will provide power for a longer period of time. It’s not going to make your motor any more powerful than the battery you have selected, it will just last longer on the same draw.

Dan

Thanks Dan...I don’t think I’ve ever used anything other than a lead acid battery in my whole life! :)

I hear ya....but a lot of AGM batteries are installed in boats these days because of their extreme low self discharge rate, their ability to take abuse, and they are spill proof. They also charge much quicker than a lead acid battery. However they are sensitive to overcharging and why you need to be careful on how you charge them if and when needed.

All my boats now have AGM batteries in them...

Dan

Right. My point was that the trolling motor, since it was used successfully on a small car battery, most not be a huge draw and, thus, the 75AH would be sufficient for L'il Buddy.

Anyone have an idea of the rough amount of time these things run on a single charge?

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Scratch that--just found this. I think 75AH with a smaller motor would be fine--at least 2-3 hours and more likely longer. I'll look at the specs when I get the motor.Attachment 15335

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AGM appear to be double the price?

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AGMs are lead acid batteries too, but they are different than the more common FLA (flooded lead acid) in that they are maintenance free and don't like overcharging (which is something you should periodically due to FLAs to equalize them). They both recharge at roughly the same rate, but AGMs can be left in a partially discharged state for a long time without the sulphation issues seen in FLA batteries. This feature is irrelevant if you are putting the battery on a charger overnight or longer after every use.

Don't discharge your lead acid battery below 50% capacity, it will damage it and reduce the lifespan of the battery. Thus, if you calculate that you need 100 AH of battery capacity, buy 200 AH of battery and consider 50% depth of discharge "empty".

Since you wrote "INEXPENSIVE" in your original post, don't buy an AGM battery. They are awesome, but the benefits they offer will likely be irrelevant for your application thus they are not worth the extra cost IMO. AGMSs are great for situations where the battery cycles through partial discharge and partial recharge cycles most of the time. I cannot fathom that happening in your application. You will very likely have plenty of time to recharge. You should just get a regular flooded lead acid battery and keep it on a charger that has a float phase every time it's not being used.

AGMs are popular for people that spend a lot of time anchored and not connected to shore power. In this use, they are often discharged to 50% state of charge and re-charged to around 80% (end of the bulk charge phase) state of charge. To get them above 80% SOC, you need to go through the absorption phase which takes a really long time and most people that anchor out multiple days in a row don't want to run a generator that long. Leaving them at 80% SOC does not hurt an AGM like it does a flooded lead acid battery.

I ended up grabbing the 90AH battery and this charger: https://www.batteriesplus.com/produc...ultra/slc10004.

The 90AH should give L'il Buddy around 2-3 hours at max, which is plenty (of actual run time). He can row, otherwise!

The charger was a bit more than I wanted to spend, but it does 6 and 12V, AGM, and a reasonable 3.8AH charge rate, so we can full charge overnight (given 70% draw).

Thanks for your help!

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