From your description and because the batteries are already 4 years old, I'm sure it is time for new ones.
According to the 2012 service manual, both your batteries are undersize and have smaller CCA ratings than the minimum factory recommendations. Minimum is 675 CCA in warm weather and 750 CCA if used in colder temperatures.
Theses minimums are for the engine only, so it is best to get the largest battery you can afford above the minimums to allow for the boat's electrical load such aslights, pumps, radios, sounders, radar, and other accessories.
Also make certain that the cables and wiring for the batteries, selector switch, and boat electrical system is correctly installed and not drawing down the unused battery.
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"There is never just one thing wrong with a boat"
--- Travis McGee
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The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. If you elect to do it yourself, be sure to use caution, common sense, and to observe all safety procedures in the vicinity of gasoline, moving engine parts, high temperature components, heavy items, and electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, correct tools, and have an understanding of how to proceed with a repair. If you are unsure or uncomfortable with a procedure, a situation or a technique, enlist the services of a factory trained technician.
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