Pick one - (xs7000 and up would be my choice) http://www.batteriesdirect.com.au/sh...FSZNpgodNRfk2Q
You pay a bit more for the ctec but I am yet to hear of any complaints besides price. I have the 4003 and it does the job on my optima d34 and bikes etc. Charging it after every use will help with its longevity.
Quoted -
" Amp draw is the measurement of electrical current drawn from a storage battery (or battery), while the trolling motor is being operated at maximum speed.
Minn Kota 's published amp draw figures represent actual on the water conditions (with all of the motor 's wiring, switches and circuitry in the electrical system as the test measurement is taken).
Approximate length of running time when operation a trolling motor at full power can be determined with a motor 's amp draw and the battery amp hour rating.
Example: A single 120 amp hour, 12 volt battery and a 12 volt trolling motor drawing 20 amps at the highest speed setting will run for about 3.4 hours.
The formula for the calculation is as follows:
.85 A.H.R. = Hours of running time. (A.H.R.= Battery Amp Hour Rating)
M.A.D. (M.A.D. = Motor Amp Draw)
As the speed setting is reduced the motor amp draw is also reduced.
A motor drawing 30 amps at high speed may only draw 5 amps at the slowest speed. The same motor that will theoretically run about 3.4 hours at high speed will run for over 20 hours at the slowest speed."