Check your battery terminal crimps…
 

I think mine wore out from removing the battery every so often.
I was surprised to see this.
Easy fix though….

https://imgur.com/a/2NlsAaD

Attachment 3135

Had the same thing happen on the starter end. Rear engine would not turn over

battery cables on boat - was amazed
 

I have a sea ray.
The battery cables were shot so I went to autozone and replaced.

A few years later, hitting starter, voltage would drop and not start.
Voltage at both ends of battery cables was the same, no drop, except under load.

Meter resistance at/near 0 ohms.

What? ???

Turned out, the cable has incrementally corroded INSIDE the insulation.
It was in dock all summer.

When high current was applied, like starter, cable resistance heated up, resistance went up voltagte at starter near zero, starter wouldnt turn.

Have used marine cables ever since.

Piper has an ad on their alum wire that had it replaced with copper

https://bsd-box.net/~mikeg/N8031W/SB_SL/SB_0836A.pdf