Avidyne has been very helpful in getting me the procedure to download the logs from the IFD540 and have them sent to them for analysis, but in the end it doesn’t seem like I will need to: The IFD cutting out was due to low voltage, as they day after the batteries were below 20V and the igniters wouldn’t even come on when they came to run it. Somehow the generators must have dropped offline on last flight (I checked on startup, but not during flight). And as voltage dropped, the IFD with it’s 16W radio cut out, whereas the Garmin with 10W continued to work. Which makes sense, as in hindsight the problem of radio cutting out got progressively, but subtly, worse. With the batteries charged the IFD works perfectly again. But this is on the ground. Somehow, stuff has a magic tendency to work really well on ground and then fu*k up in the air… 
It’s a little strange the whole affair, as I landed in Paso Robles I had to motor the left engine on the starter (with the igniters off), to cool the core down from 300C to 200C degrees, which is max start temperature to avoid hot start. It spun up quick and cooled everything down and when it was below 200C I put the igniters on and she started up fine, well below max temp. That’s not what you’d expect if the battery had been depleted – then she would have run much hotter, taken longer to spin up and potentially had a hung start. So to then go from that to having completely depleted batteries 45min later is a little odd, but I guess that last start could have been the straw that broke the camels back, so to speak. We’re putting solid state regulators/relays in now, as the generators are newly overhauled and batteries are new.
