Battery size for my 20hp Johnson electric add on

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user 21074

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I am making slow progress in putting in my electric start.Finally got my stator and rectifier on,starter-solenoid and bracket assy needs on along with switches and Decideing what battery to use and want to save space and weight.I saw where someone actually used a lawn/garden battery to start his motor..I also was checking out a jet ski or motorcycle battery.I am only using it to start motor on my 14’ Jon at this point since everything else has been on my deep cycle for a long time.
 
If you're only using it to crank the motor, I'd just run over to Walmart and grab one of the $29 lawn mower batteries. Should work fine.
 
I use a U1 lawnmower battery for my Yamaha F25. Also previously used it on a 30hp Yamaha 2 stroke. No issues for either one.

I assume you also have backup pull start since its a conversion, so even more reason to go small as possible.
 
Yes have rope start also.Just got done with conversion and took my battery off of riding Mower and it crank no problem.Charging circuit seemed to be working as I did see increase in voltage while increasing rpm.Was on muffs so couldn’t take it too high.I was concerned about the starter since bench tested only the gear popped out but right back in.Guess they have to be engaged to stay up.Was not sure about that since I had another used one doing the same thing.Only other concern was the timing stopper for the high end. Bracket I used was from a 35hp (34*)so the screw was not adjusted for my motor(30*).Made some measurements and put it at full throttle and locked the stator plate in position best I could and took old bracket off and put new starter and bracket on and it was off so adjusted and thought about doing the Joe Reeves Timing method which can be done out of water to see if it is ok?Just need to get it on the water and hopefully that is the last step and engine doesn’t blow..thanks for the input on battery.
 
newyota said:
Yes have rope start also.Just got done with conversion and took my battery off of riding Mower and it crank no problem.Charging circuit seemed to be working as I did see increase in voltage while increasing rpm.Was on muffs so couldn’t take it too high.I was concerned about the starter since bench tested only the gear popped out but right back in.Guess they have to be engaged to stay up.Was not sure about that since I had another used one doing the same thing.Only other concern was the timing stopper for the high end. Bracket I used was from a 35hp (34*)so the screw was not adjusted for my motor(30*).Made some measurements and put it at full throttle and locked the stator plate in position best I could and took old bracket off and put new starter and bracket on and it was off so adjusted and thought about doing the Joe Reeves Timing method which can be done out of water to see if it is ok?Just need to get it on the water and hopefully that is the last step and engine doesn’t blow..thanks for the input on battery.

Nice. So can that specific model be converted to a 35 hp?
 
wmk0002 said:
newyota said:
Yes have rope start also.Just got done with conversion and took my battery off of riding Mower and it crank no problem.Charging circuit seemed to be working as I did see increase in voltage while increasing rpm.Was on muffs so couldn’t take it too high.I was concerned about the starter since bench tested only the gear popped out but right back in.Guess they have to be engaged to stay up.Was not sure about that since I had another used one doing the same thing.Only other concern was the timing stopper for the high end. Bracket I used was from a 35hp (34*)so the screw was not adjusted for my motor(30*).Made some measurements and put it at full throttle and locked the stator plate in position best I could and took old bracket off and put new starter and bracket on and it was off so adjusted and thought about doing the Joe Reeves Timing method which can be done out of water to see if it is ok?Just need to get it on the water and hopefully that is the last step and engine doesn’t blow..thanks for the input on battery.

Nice. So can that specific model be converted to a 35 hp?
Yes..You can put a 35hp carb and intake on it from what I understand.Actually sold the carb and intake and lower unit from the 1977 35hp parts motor I bought for electric parts to a kid that wanted to convert his 25hp to 35hp.Got my money back👍
 
A good quality UTV battery will work fine, even smaller than a lawn mower battery. I have a " MAX " wheel chair battery, same size as my UTV battery, I use it to power my 30 gallon lawn sprayer and my 28lb trolling motor in my pond jon boat. Had the battery for almost 6 years, no issues. Fully sealed so it can operate in any position !!! Best part it costs less than 40 shipped to my front door!!
 

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