Dead battery, jumped, ran weird and died

[Liamfm]

Last night I accidently left my ignition switch on in my 97 sport. Battery was very very dead today. Jumped the boat from another. Went out onto the lake but it ran kinda rough. Almost like a misfire or timing off. Not enough to warrant me turning back, but I did begin to notice a lack of power. Eventually the boat died at idle. During this time I was showing about 14.5v which seemed high, but I attributed to the alternator working to bring the battery level back up.

We put another battery in it and got nothing. Zero. Not even a light on the dashboard.

Switched back to the original. Nothing. Then out of nowhere it comes back to life. Started up. Ran great.

We ran it for about an hour. At the end I went to start it again and it started right up. During this time the engine ran normally. Lots of power. We even went ahead and turned on the stereo.

So my question is, why did it run so poorly after the jump start, and to the point where it shut down. Almost as if it doesn't have enough juice to run the computer or whatever. And why when it died out did we get nothing. No power. And then it just came back to life?

Gt40. Fingers crossed no issues. Left a trickle charger on overnight.

Battery is an interstate AGM about 2 years old.

[bturner]

Hard to say without being there or seeing anything. My first guess based on very limited knowledge about the boat, maintenance or current condition would be wiring. The boat is nearly 30 YO. If it were mine and I had an issue like this I fall back on the advise I've given on this and other sites about grounding and connections. That would be to go through the primary connections and most likely swap out the primary ground and positive cables on principle alone.

It is also quite possible you inadvertently bumped or moved the safety lanyard which depending on the boat would give you the no power condition you experienced. If you have this issue again, that would be the first thing I would check or eliminate from the starting circuit.

[Liamfm]

Thanks - Boat is maintained to near 100%. Darn near mint. Cables are <2 years old. The original issue was 100% user error (left the ignition button on overnight). The odd part was what it caused upon jump starting (felt like it was running on 7 cylinders, or timing was off).

Certainly wasn't cables or the safety. I do think there is a chance that removing the cables allowed the computer to 'reset' and then upon restart it worked flawlessly. Something during that jump told the voltage regulator to allow the alternator to charge at 14.5 or higher, and for the computer to not exactly run the engine all that well. Then it just died out at idle after about 30 minutes (which has NEVER happened). Then, an hour later, after dinner on the lake and some swimming, we swapped batteries. Still 100% no lights, nothing. Swapped the original back to get towed in, and bam, ignition and blower worked, started a touch slow, but not bad. Ran perfectly for the next hour, radio on, nav lights on, etc. Shut it off at the lift, started right back up.

So if it were a connection issue that would be:
connection was good enough to jump it and run for 30 min, but then die
2nd battery connection was no good
original battery connection was no good, then, moments later, good.

Perhaps one of life's unsolved mysteries. We shall never know. By about 5:30pm today, I hope to check it again, and expect it will be perfectly fine.