Try using a group 31 deep cycle battery instead of a starting battery. Deep cycle batteries are desinged to be dischrged more deeply than starting batteries and have more reserve power because of their thicker plates.
If there is room, installing a deep cycle battery just for your pumps and electronics would eliminate your starting battery from running down during the day. Evinrude has an accessory auxiliary charging circuit that connects to the "house" battery and charges it independently from the starting battery. See your dealer for more information.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with 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, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.