More battery questions

[Kirtley Howe]

My outboard motor will charge the starting battery when the motor is running. So, why would it be necessary to have a deep cycle starting battery? Why not just use a good quality standard battery to start the outboard? With my use, I would only be starting the outboard 3 or 4 times a day at most, and then running a fair distance so the battery should be recharged by the motor.   My fish finder is a pretty basic unit which does not draw much power, so unless I am running lights, the draw on the battery is minimal. Of course, the trolling motor needs a good deep cycle battery that is not tied to the starting circuit. 

[Tennessee Boy]

I agree.  If all you’re running is a small FF and minimal use of other accessories then all you need is a cranking battery.

[Jig Man]

That has been the norm for a long time.  It has only been the last few years that sonar units have gotten so powerful that a regular cranking can’t handle the job.

[Woody B]

Batteries, and battery types are complicated, but don't necessarily need to be.  I spend real money on a trolling motor battery, but use whatever for cranking.  (50 horse motor though).   However, I recommend either keeping a jump box or a set of jumper cables in your boat.   I keep a NOCO GB 40 in my truck, and transfer it to my boat when I'm fishing.   

[casts_by_fly]

just remember the difference between the two types of batteries.  A cranking battery can deliver very high amperage very quickly.  That's important for turning over bigger motors, especially if they are older and have trouble turning over (which you should get fixed, but that's another story).  Deep cycles are for slow drains of amperage over a long time.  Physically, the difference is the plates inside the battery.  A fast, high amperage requires a lot of surface area of lead on the plates in contact with the acid/gel mat.  Every time you use the battery, you're pulling some lead off of the plates.  Recharging puts it back on.  If you reduce the plates too far, there is nothing to put the lead back onto.  That's the cause of permanent damage regardless of battery type.

 

So if your fish finder is drawing a negligible current (like a piranha unit) then you're just fine.  If you're hooking up a live scope unit, then you probably aren't.  In your case you shouldn't need a separate battery.