Step A: Test the battery with lowest charge first. Ensure battery switch is off. This will be your baseline voltage. If less than 11.7 vDC, charge battery for several hours with a smart charger. Retest voltage.
Step B: Next turn the battery switch to the lowest battery. Measure and record voltage. This will ID parasitic drain voltage.
Step C: Turn on ignition and let systems fully boot up, approx. 30 sec. ensure audio, lights, pump systems, blower, are all turned off. Record voltage.
Step D: Turn ignition off and select power off on control system. Wait 10 sec, then turn ignition back on and let system boot up, blower run. Audio, lights, pumps should be off. This is your pre-start voltage. Measure and record. If low battery is below 11.7 vDC, battery should be replaced.
Step E: start engine and record voltage input. At idle, voltage should be 13.7-14.4vDC. If not, check alternator connections to battery switch/bus bar. If no issue, and voltage is 12.9 vDC or less, have voltage regulator on alternator tested, and assess for engine / fuel system shorts and bad connections, then move on to next step. Goal is to have idle voltage between 13.7-14.4.
Step F: at idle, engage pumps for 5 min. Record voltage. If voltage at battery drops below 11.7 vDC and remains after pumps are shut off and engine at idle, there is a short in the pump system. If voltage returns to 12.9 or better, system is ok, but not performing optimally. Isolate and assess any parasitic drains. Clean/replace/tighten connections.
Step G: at idle, run audio system for 10 minutes at volume you would usually float with. If voltage drops below 11.7 vDC and remains after audio is shut off and engine at idle, there is a short in the audio system. If voltage returns to 12.9 or better, system is ok, but not performing optimally. Isolate and assess any parasitic drains. Clean/replace/tighten connections.
Repeat with Bat2.
Idle voltage 12.9 or less suggests poorly performing alternator, voltage regulator, or circuits. Cycle all breakers and ensure no partial disconnects that may be causing resistance. Check belt condition and tension, pulley tightness, etc.
Unequal idle voltage between battery banks may indicate failure in charge circuit or battery switch / bus bar. Repeat test with Bat1 or Bat2 physically disconnected. If voltage returns to 13.7-14.4 replace disconnected battery as a cell may have collapsed.
If none of this results in diagnosis or solution, the gremlins may be deep. Seek professional help and good alcohol to absolve your frustrations.
Currently boatless
