I'm not trying to bust your chops at all, but looking through your thread, you used an electronics tray with everything packed in there pretty tight. Glass fuses, regulator, battery, etc... What I'd suspect is either a battery shorting or as I said, a regulator losing control of the alternator's charge and allowing more than 15v at the battery.
After you unwind and the adrenaline and frustration subsides, let's check through your electronics component by component to verify proper function and safety. You surely don't want to pass along something you've built that's unsafe. You've taken too much pride in your build to live with that.
If it makes you feel less Sh!tty, I finished my 550, three days later, my boy "gently wrecked" it. 1.5 years, $8k and now another $1500 to fix it. Not to mention 4 months of delays. I know your pain... And we are not alone. But they can be fixed and everyone lived through it.