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You do need a deep cycle battery. They come in different group sizes, 24, 27, 29 ect. The bigger the battery the higher the number group size. The bigger the battery, the longer it will run before it needs to be recharged. Also, the bigger the battery the more expensive it is going to be. The best answer is to buy the biggest battery you can afford.
a 28lb thrust motor is going to draw roughly 20 to 25 amps on its fast setting. Here is a deep cycle from sears that I will use as an example.
That battery has a 200 minutes reserve load time. At a 20 amp draw you should get the full 200 minutes run time out of the battery, at a 25 amp draw, the run time will be less.
The next part of it is you really don't want to use a solar charger to charge the battery. The battery simply will not last. What you want to do is run this battery as dead as you can possibly kill it, and then when you get back in throw it on a quality charger and charge it back up. And you want to throw it on the charger when you get back in fishing for the day. Not the next day, and not the next week, but that night. If you don't charge them like that, you will be likely if the battery makes it a season. If you charge them the right way, then you will get a few years out of a battery. So when you set your budget, budget in a decent battery charger.
Post back if you still have questions on this.
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So cranking amps don't matter? just the group #?
Local fishing store had 4 batteries. $99 to $195. But the cheapest one said 1000 amps then the next was 690, then 750 and then 870. Didn't seem to make any sense at all. The last three all had more cold crank amps for more dollars but why would the Interstate 24MxHD be cheaper with more amps?
Engine says at 28 lbs a 105a battery should last 3 hours. Clearly that 105a isn't amps ??? I'm confused.
Have to run... wife booked diner. Will definately be very happy to pay for your time. Last Q was just if you have a personal brand recommendation or is it all just about the price? IE: Die Hard, Interstate...even WalMart's brand. Is there one that you personally feel is best? Don't do any research on that... I know it wasn't really in the original Q so just off the top of your head... Thanks again.
Cranking amps don't really matter in your case because we are not cranking over an engine, just spinning a little trolling motor.
The bigger a battery is, the more lead and the more acid is going to be inside of it. The more lead and acid, the more power, both in cranking and reserve.
What you need to look at is not the cranking amps, but the reserve capacity. And that will vary size by size. The group size is not the capacity of the battery, or its power, but just its physical size in height, width and depth.
When you go to the stores to look at the batteries, don't even look at cranking amps, because it just does not apply to you. (we are not cranking over an engine) Look at reserve capacity. Reservice capacity is how long a battery can supply current (amps) before the voltage drops. Most batteries are rated at 25 amps. So the battery I gave you above had a 200 minute reserve capacity. At a full 25 amp draw, the battery should last 200 minutes before it needs to be recharged. Compare batteries by size and reserve capacity.
All batteries, both starting type and deep cycle types will list both cranking amps, and reserve capacity. A starting type makes good cranking amps, but has little reserve. A deep cycle will not deliver as much cranking amps, but it will have a lot in reserve. They are opposites.
I am copying and pasting this from a battery FAQ that I keep. But here are more or less textbook definitions between the battery types.
Let me know if you still have questions about this.