Not unreal. For example, some leakage could be between
wires inside an electric box that become more conductive when
humidity increases. Not conductive enough alone to trip a
GFCI, but conductive enough when combined with leakage from
the laptop.

Also the battery charger was on - but was it charging when
tests were conducted.

All appliances have galvanic isolation. That means (in
theory) low voltage circuits are isolated from AC mains - not
leakage. In reality, even galvanic isolation has microamp
leakage. I have even seen where a low voltage light causes
just enough leakage to create rare and intermittent GFCI trips
only when other appliances were powered just because a
chipmunk chewed into insulation of that low voltage (and
buried) wire.

You have a battery charger on the circuit. How much is it
leaking? The numbers, such as the normal leakage into safety
ground wire where that safety ground wire connects to breaker
box, are so important to those who would answer your posts.

Again, what was humidity then verses today? How long since
the last rain or a last boat hose down? And even what was
powered from the battery when you were testing previously?
Search for alternative circuits for current leakage - and that
even includes the battery charger. GFCI says you have leakage
somewhere. Now all we need do is find that leakage. Its easy
to say - and so damn difficult to put into reality.

Nothing unreal about your problem. Have solved these things
so many times that I have no belief in ghosts. But then
others long since give up before I do. My sympathies for your
frustration and my envy for your challenge.

JohnHH wrote:
No, NOTHING was plugged into the computer. Certainly no NMEA
devices. That said, I probably lied; I use a wireless mouse
that MAY have been plugged in to a USB port every time.

The laptop is a SONY VGN-A190 with Sony AC brick with a 3 wire
plug. In a year of use, I cannot remember it ever starting up
without tripping the GFI - EXCEPT TODAY!

This is totally unreal. I came up to the boat this afternoon
and made sure everything was turned off and nothing else
plugged into the AC - only the ships battery charger was on,
even the DC was off. I fired up the AC outlets and tuned on
the computer, No fault. I turned off the computer, turned
everything on and tried again. Still no fault I tried 4
times and can't cause it to fault. I'll try again in the
morning after it has been off over night.