Gonna try to give a run down of what has happened in the last year or so ...
Spring 2013- trim up relay went out
June 2013-interstate starting battery went dead , replaced with 1000 cranking amp interstate

Summer 2013- steering cables went out and boat sat till December 2013
December 2013 - got new cables and within weeks the lower voltage regulator went out , I replaced it with a factory mercury part.
March 2014 - started noticing that after fishing for an hour or so the voltage seemed really low on starting battery and you would have to fast idle the motor just to get it running ...
May 2014- took new interstate in and it failed a load test so they replaced it .
June 2014- was out last night and the boat seemed to charge from 12.5-14.2 volts until it got warm and sat for a while ... My run back to the ramp last night the motor was putting out 0 volts , the motor runs great while not idling but once it goes to idle and the voltage gauge drops its hard to keep it started

Any ideas as to what is going on ?

Bump .... Any body got any ideas on where to start looking ?

Stator ? Regulator ?

Just had a boat acting the same way. Found a bad ground where the Stator, trigger and another wire goes to ground on the aluminum plate above the starter solenoid. Remove and clean all grounds, put dielectric grease on all connections.

Check all three pieces. Regs can take out a stator and vice versa! Check tha bullet plugs for overheat, melting and etc. Stator needs ta be checked with a dva for a true diagnostics. Sometimes an ohm reading will show it and sometimes not......This if what Gary says doesn't work.

Ran it in the driveway for the last 2 nights letting it get really warm ... It runs great at idle putting out 12.8volts at the battery .... After it gets warm it will idle up really quick and die ... Fires right back up , runs for a minute , idle jumps up to 1k and it dies ... I've checked all grounds and ohmed out both regulators ...

"0" is stator output pretty much indicates tha problem if rects/regs are good. back ta square one. battery needs ta be "load" checked. stator needs ta be checked. ecu really needs minimum 12.5 volts. won't do right without it. might be a fuel delivery thing also which low voltage can cause ecu ta make electric high pressure pump act funny too. you can "temporary" 12v. with tha purple wire and ground to tha pump. be sure ta disconnect tha pump feed from tha ecu. tha purple is a "switched" hot with tha key. this is just to test, not permanent. if it seems ta straighten up on tha hose ya need ta put in tha water, in gear and check with a load on it.

few other things but I would do these first......

oh yeah. first thing before any of tha above. start it and as soon as it starts ta go down pump tha bulb quickly. if bulb is hard and it dies start it again and push tha key in when it starts ta die. if doin' either of these things keeps it runnin' indicates mech side fuel delivery problem.....might not be total problem but does contribute to it.