Low voltage light and battery please help

[Jay anstice]

I have a 2012 Seadoo SP 180.with about 130 hours on it. We were out yesterday and went to start the boat and the battery light lit up and low voltage came acrossed dashboard. Then shortly after check engine light came on. Everything seemed like it was running perfectly fine started the boat fine just like normal.
Checked battery 1 today, it seems a little on the weak side but I do have a dual battery setup and we switch to battery 2 our on lake I still had the same problem. Main battery does drop down to 11.9 after boat is shut off. Nothing is draining it is just the battery itself that does this. Could this be the problem?
Now I am testing it out of the water. when I start it up with water hose directly to engine. I don't get the check engine light or battery or low voltage on the dash information center. Everything is running fine. Anyone have any ideas please help thank you!!

 

[10forty2]

May be a bad connection. May be a bad alternator. May be the voltage regulator. Check the voltage of the battery without the engine running. Should be right at 12VDC or slightly more. With engine running, the voltage should be 13.5VDC - 14VDC or slightly better. If the voltage doesn't increase when the engine is running, you either have a bad regulator, bad alternator or it may be as simple as a bad connection somewhere.