2004 z300txrd

So I noticed today on my gauges that my voltage dropped to around 11. When I would trim it would drop to 9 and at one point cause the boat to loose power. I made it to a Marina got fuel and started to leave. Boat went into gear but shortly after died. All instrument displays went out too. Checked the batteries and noticed they were dated 2016. I changed one of the batteries out and it started. I let it idle for a few minutes and then the instrument displays go out followed by the boat shutting off. I made sure I had the new battery selected on the switch. A short time later the displays would come on but but would not start, not even turn over. Any suggestions on what to look at next. Oh I forgot to add. When it was idling on the new battery, the volts would fluctuate between 12-13.4 volts.

Check battery connections for cleanliness and tightness. At both ends. Check any other cables that are connected between where the battery cables attach to the motor and on from there. Particularly to the rectifier/regulator.

Test the rectifier/regulator for proper output voltage.

I will check that. Thanks.

boscoe said:

Check battery connections for cleanliness and tightness. At both ends. Check any other cables that are connected between where the battery cables attach to the motor and on from there. Particularly to the rectifier/regulator.

Test the rectifier/regulator for proper output voltage.

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Update: I have gone through the wiring and replaced both batteries. I didn’t find anything noticeable on the wiring.
same issues still going on. When i go to start the boat the displays go away and nothing happens it will do this several times then the boy will start. Voltage still drops a lot when I trim the motor. Any other suggestions on where to look/ diagnose. Thanks again!

If the voltage drops it has to be a battery issue or a wiring/connection issue. Usually the latter.

Do you know how to do a voltage drop test?