Hey 1blue,
Glad to help where I can.
On that note, I by no means am an expert in the battery world. I know just enough to get me in trouble
With that being said, here's some info I've used to help me figure out amps,volts, run time, etc.
Reserve Capacity (RC) is the number of minutes a fully charged battery at 80 o F (26.7 o C) is discharged at 25 amps before the voltage falls below 10.5 volts. To convert Reserve Capacity (RC) to Ampere-Hours at the 25 amp rate, multiple RC by .4167. More ampere-hours (or RC) are better in every case.
For example, if your trolling motor is drawing a steady 20 amps and you want it to last 1 hour you would start out with Step 1:
C=20 amps * 1 hour = 20 AH
Then proceed to Step 2
C’ = 20 AH / 0.8 = 25 AH
Then take the high rate into account
C’‘=25 /.5 = 50 AH
Thus you would need a 50 amp hour sealed lead acid battery to run the trolling motor for 1 hour at 20 amps average draw.
Im sure this is clear as mud now. Lol.
Look up Lou r Pitcher here. He definitely seems to know his business when it comes to this stuff.