For shits and giggles I pick up an 12' inflatable with motor bracket and a 50 ft pound thrust trolling motor.  Plans are to use it in the back bays and estuaries, along with some slow current rivers.

The inflatable is rated for 5 people (up to 1300 lbs), however it will only be used by 2 people and a dog at any given time.  So I am think max load will be no more than 500 pounds..........really depend in the amount of beer we bring.

So what amp hour rating battery do you think I need as a minimum.

TIA

Depends on how long you plan to use it, how much wind there is, and what speed you want to go for how long.

I had a 55lb Minn Kota on my fiberglass bass boat with the large size deep cycle battery you find at the Farm and Fleet stores....I never ran out of battery and did quite a bit of trolling...6-8 hours on speeds 1-2-3 with bursts of 5(fastest it goes)...

Googling around says 55lb thrust trolling motors are around 50amps max draw....so that's probably when the boat is at a stand still and you switch it to high.  It should drop off as the boat speeds up and resistance drops off.

So even at max output, a Group 27 Deep cycle battery around 100AH capacity should be able to run the trolling motor on max output for 2 full hours.  4 hours at half output, this would be my guess on draw at speed in top output.  This is only a guess...it's probably lower than that.

The motor should have a decal with the amp draw on it. Use that as a basis and do the math for the battery size.

A 750 AH -ideally deep-cycle- battery should be more than sufficient for your needs.

750?  Good lord....how big of a battery is that?  Even the semi-truck batteries I've seen aren't even half of that capacity from what I remember...like 220AH (I can't remember exactly)?  They're monstrous.  Most trucks run 3?  At least the ones I've seen do.  No way you're going to fit that many batteries in a boat his size.  Nor is it necessary.

My bad... meant cranking amps.

Ah...that makes more sense.

Cranking amps is not what is looked at for a deep cycle trolling battery.

He needs reserve amp hour capacity. OP, buy the largest A-hr battery you

can afford and physically fit in the battery compartment/box.

I've never heard anyone say they bought too large of a battery for a trolling motor.

Pretty solid advice right here.

Think I made out lie a bandit today.

Picked up a Diehard Marine Gold 27M group 12V 95AH deep cycle battery for $139.  Sear has a 25% off automotive promo today.

The real bonus is that I earned $126 in bonus cash on a future purchase store wide.  Will be using that money to buy a utility box to store the battery and other gear.

Just bought a 29DC battery from Walmart for $99 that fits in a minn kota battery box. 2 yr warranty. This will power a55lb endura max minn kota. Had it out twice and seems like a good buy.