Boat electrical problem

I have an issue that’s driving me nuts. For a while now give had issues starting boat. Yamaha F150 2014.

It seems electrical because after sitting a few days, when I turn the key it acts like the battery is near dead. I will get the oil light and temp light on and maybe a flicker of the gas gauge but otherwise dead.

Usually if I turn the key about 5-6 more times it will eventually start. Once it starts, it will keep starting on first turn for at least the rest of that day if not another day or two. Then the same acting dead after sitting.

I’ve changed the starter assembly and starter relay. I thought for sure it was battery going bad but it tested good and also tried another good battery and it did the same thing. I thought for sure it was battery because when it was acting dead and I never got it started, I did nothing but charge the battery and it cranked right up when the charger showed full.

Only other possible factor I know is that a while back I was having electrical issues that seemed like bad ground, wasn’t even getting a flicker when turning key, so I changed the ground cable out with a 2 gauge cable from harbor freight but after that it seemed to work great for a while.

Sorry it’s long but any ideas where to look next? Thanks