Didn't go flying today.
The CFI was a little amused by the thoroughness of my preflight inspection - but when you take an unfamiliar aircraft, and put it in the hands of someone who has rebuilt one, there's a lot more things that I now know can be cattywampus to check. Example 1: They'd never had a student check that the ignition wires were firmly attached to the spark plugs. (Look, it only takes once, okay? I learned that lesson from somebody else's exciting flight, and now I check every time.) Example 2: I identified the "we can't find that oil leak", and pointed out that it was very clearly from which spot on which seal on which cylinder - which means that fixing it would require cracking the engine. Given it is a very minor oil leak indeed, I can translate the mechanic's "can't find" quite clearly as "Don't want to crack the engine to fix."
The CFI was less amused when I pointed out previously unnoticed hangar rash that needs fixing.
But be that as it may, no preflight reveals the dead battery. That waited until we got in and pressed the start button, and got a single click from the solenoid as reward. So, we got the plane jumped. Now, once the plane is jumped, there's one instrument that needs extra special loving attention on the checks, and that is the ammeter. It should read as solidly charging the flat battery.
This one didn't. It didn't show as discharging (ie, dead alternator and we're running on the freshly jumped battery), but it didn't show charging, either. Hmm, I thought, that's hinky. Either the ammeter isn't working, or something's funky with the alternator. Better keep an eye one it, especially on the runup.
Three minutes later, as we were rolling toward the runway, the GPS and the Com Panel went dead. Yeah, my apprentice mechanic skills are saying that alternator's either dead, or putting out so little power that we're draining the freshly-jumped battery past the point of sustaining the heaviest electrical load (the big glass screen and high-powered GPS avionics.) My CFI, who has the mistaken impression that I fly no radio because I fly one of those ancient taildragger-type airplanes, leaned forward and shouted (Com panel dead means the headsets don't work.) "I know you're used to flying no-radio, so I'll give you the option of continuing the flight!"
I looked at 'em like they were asking if I wanted to tango with a thunderstorm. "Unfamiliar airspace, unfamiliar airplane, no comm, no electrical? No way!"
So we taxied back to the mechanic's hangar, and waved one over so they could see what was going on. He leapt up on the wing as we slid the canopy back, and I pointed out the dead GPS, dead com, and the backup nav/com and transponder were still live. Then I asked (or shouted, over the engine and prop), "Beacon is switched on! Is the light on?" This is one of those helpful cross-check things, because the beacon is wired to the master switch, not the avionics master. It wasn't - there's enough juice to run the surviving avionics, but not the lights. Definitely sounds like an alternator that's putting out just enough juice that it tests fine under no load when tapped with a voltmeter - but not enough to power the lights and avionics and charge the battery at the same time. Ah, intermittent electrical issues, how I hate thee.
So I shut her down, and rescheduled.