Do I need a cranking battery?

Depends on the size of your motor, but they are 2 different batteries for 2 different purposes. Cranking battery is for quick strong burst of power and deep cycles are for slow long draw. I would definitely have a cranking battery on anything bigger than a 25hp motor. Get the biggest one you can.

I ran a single battery for many years. Did not use the electric motor for long sessions like a bass fisherman. But with my 30 hp Evinrude I could remove the hood and wind a starting rope around the flywheel if needed.

1. What else is drawing power from that battery?
2. How old is the battery?
3. What size is the battery?
4. What voltage is it putting out?
5. Is the battery properly maintained? (Clean terminals, never discharged below 50%, always charged immediately after an outing, water level monitored.)
6. What outboard are you cranking with it? A new fuel-injected 50-hp 4-stroke fires up with just a turn of the key. An old 200-hp carbureted 2-stroke needs lots of cranking before it fires up.

Thanks for all the quick responses-I have a 25 hp 2 stroke-usually charge right away after use -Better check the water level this morning.

Can go have it tested.

What’s not working so well on it in particular?

If all you are doing is starting the motor, a cranking battery will be fine. If you are also powering livewell,baitwell,electronics, stereo, running lights for extended periods of time, a deep cycle battery will serve you better. A deep cycle will start your motor for years and run everything attached to it, a cranking battery will start your motor for years but will not run everything else as long as a deep cycle will. In a weekend of fishing, how long are you actually turning the key and cranking the motor, if the motor starts like it should, most likely less than minute or two at most.