I unplugged my boat and the cranking battery drained in a couple of days.  The power switch at the  console is off and I did a drain test by taking out each fuse but that all checked out.  I thought I read somewhere that a bad alternator might do that when it sits, but I can't find the article, so not sure if I remember that correctly.  Any suggestions?  And thanks in advance...

How old is the battery?

about two weeks old

 

the only thing I've done to the boat in the last couple of months is add a trim blinker switch

 

Drained without the motor running or after using the boat? 

10 hours ago, warrior1 said:

about two weeks old

 

the only thing I've done to the boat in the last couple of months is add a trim blinker switch

 

I'd check there first.  Make sure you didn't leave any exposed wires touching any metal or reverse the positive and negative on that switch or on the lights.  Either could ground out the positive terminal and cause the drain.  Plus, everything worked fine up until then, so that's the most likely place to find the culprit.