Which battery for electric motor?

[Rallendk]

Hey there.

Im about to buy a "Shakespeare Sigma 54 LBS Saltwater" Electric motor.
Shakespeare Sigma Electric Outboard Motor

Im really confused about the different battery types though. Some people are talking about AGM-types, while other people are talking about "marine batteries". What should I aim for? And which size would I buy?
The motor should supposedly run about 1.5hour on full speed and about 7-8 hours on low speed, with a 75 AMH battery.

Experience and comments about the motor would be nice aswell. Thanks already!

 

[JB]

Re: Which battery for electric motor?

After several disappointing experiments I settled on Walmart's Everstart Marine Maxx, the big yellow one. It is a dual purpose.

I used only one battery for everything and the big yellow one did the job. Definitely the best bang for my bux.

If you plan to do a lot of trolling without charging periods you might do better with their biggest deep cycle.

You can spend a lot more without getting much more service.

 

[Silvertip]

Re: Which battery for electric motor?

Forget AGM. All you need is the largest "deep cycle" you have room for and your budget allows. A group size 27 is the minimum size.

 

[Rallendk]

Re: Which battery for electric motor?

Thanks for your inputs! Why wouldn't I use the AGM type? It sounds like the "new" stuff to me..

 

[Silvertip]

Re: Which battery for electric motor?

Thanks for your inputs! Why wouldn't I use the AGM type? It sounds like the "new" stuff to me..

All you need to do is look at the battery specification label and then look at the price tag. You can buy two standard deep cycles for the price of one AGM and the specs are the same and in some cases better on the deep cycle. Properly taken care of the deep cycle will also last as long as the AGM. "New stuff" as you call it does not necessarily make it "better stuff". People simply don't know how to shop for stuff. Go to your local farm store if you have them in your area. Fleet Farm, Farm & Fleet, etc generally have an automotive section. You can buy a group 27 deep cycle for $75.00 and even lower when on sale. A group 29 or 31 for just a few bucks more. A group 27 generally has a RC (reserve minutes capacity) of 170 - 180 minutes at a discharge rate of 23 or 25 amps. What that means is the battery will deliver that current for the specified minutes. Your 54# motor will draw a maximum of about 46 amps so it is twice the specified discharge rate on the battery. That means the battery referenced will run your motor for 1.5 hours at maximum current draw. Maximum current draw is rarely reached since that number only applies to a fraction of second during initial start and when the rotor is stalled -- as in tangled with weeds. Now I ask you -- why would you spend 2 - 2-1/2 times for a "high-tech" battery that has the same or very close to the same specs? Oh yes -- you can tip it upside down. Whoopee. Read the labels and understand what you are looking at.

 

[Rallendk]

Re: Which battery for electric motor?

All you need to do is look at the battery specification label and then look at the price tag. You can buy two standard deep cycles for the price of one AGM and the specs are the same and in some cases better on the deep cycle. Properly taken care of the deep cycle will also last as long as the AGM. "New stuff" as you call it does not necessarily make it "better stuff". People simply don't know how to shop for stuff. Go to your local farm store if you have them in your area. Fleet Farm, Farm & Fleet, etc generally have an automotive section. You can buy a group 27 deep cycle for $75.00 and even lower when on sale. A group 29 or 31 for just a few bucks more. A group 27 generally has a RC (reserve minutes capacity) of 170 - 180 minutes at a discharge rate of 23 or 25 amps. What that means is the battery will deliver that current for the specified minutes. Your 54# motor will draw a maximum of about 46 amps so it is twice the specified discharge rate on the battery. That means the battery referenced will run your motor for 1.5 hours at maximum current draw. Maximum current draw is rarely reached since that number only applies to a fraction of second during initial start and when the rotor is stalled -- as in tangled with weeds. Now I ask you -- why would you spend 2 - 2-1/2 times for a "high-tech" battery that has the same or very close to the same specs? Oh yes -- you can tip it upside down. Whoopee. Read the labels and understand what you are looking at.

Well, I think I get your point! .. It's a lot more expansive in Denmark than the prices you mention, though.
Would I look for anything else than a deep cycle battery around 75AH? Or should I just choose the cheapest one? Im not sure the group thing is used in Denmark..
And would about a charger?

Bonus question: I live in an apartment. May I charge such a battery inside? And what about the gasleak when using it?

 

[Silvertip]

Re: Which battery for electric motor?

Yes -- you can charge the battery in your apartment. Just don't do it with the battery adjacent to an open flame. I don't know what battery types you have in Denmark but the name "deep cycle" applies to battery construction that allows the battery to be repeatedly deeply discharged without damage. Deeply discharged does not mean discharged to zero. Repeatedly discharging a deep cycle battery beyond 50% will greatly shorten it's life. Automotive or starting batteries (marine rated or not) are designed to deliver very high starting current for a very brief period without damage. They are not designed to be deeply discharged as would be the case with a trolling motor. AH rating RC (reserve capacity) mean essentially the same thing. 75 Amp hours means the battery would delivery 1 amp for 75 hours, 75 amps for one hour, or 37.5 amps for 2 hours. Use those numbers along with the 1/2 speed of the trolling motor drawing roughly 25 - 28 amps to determine actual run time. The key point here is you really need a "deep cycle" battery. Yes - a standard auto or starting battery will work but it is not intended for that type of service and will be short lived. Batteries are like buckets of electricity. The larger the bucket (AH or RC) the more capacity it has and the longer it will run a load.