Could I have gotten another bad one? It does not combust, but could I have coil alignment issues or something? .
Sorry to hear you are having a frustrating time, Petey. Yes, you could have another bad one, though "bad" may be a judgment call given your issues. Coil alignment could easily be the culprit.
Is it possible to tell from the serial number if they sent me an earlier version (it came with the older battery)?
Not enough to be meaningful. I think the ones from 2014 start with "14" as the first numbers. But that doesn't help much.
Are there things I can try on my own without going through more hassle with Firefly? Or does this behavior fall within the normal variations among units?
There are of course a myriad of technique tweaks that change the behavior of the FF. If you've tried all the variations (check the "best of" thread for ideas if you haven't already) you may have a malfunctioning unit. It's not obvious to me that's the case, because the problems you are having
do fall within normal FF behavior, sort of.
1. I have two FFs currently, and they have noticeably, even drastically different resistance. One has a stronger magnet than the other, noticeably. (That's the one with the easier, less-resistant draw, oddly.) Both perform fine, but differently. One is hotter than the other. Yes, there certainly are differences between units, and yes, no two seem identical in the way they perform, to me anyway.
2. The "harsh" thing isn't something I've experienced, other than the odd session here or there. Certainly nothing systemic or consistent. The thing is, I'm not sure it's evidence of device malfunction. If it were running too cool, even pulsing the button shouldn't make it harsh, just maybe normal in extraction. If it were too hot, you'd probably be combusting if you pulse that button.
3. Sticking a pin in the plate holes won't tell you anything and there's not much space between that plate and the ceramic platform it sits on, so your perception that you couldn't get a pin through it isn't indicative of much. Doesn't mean anything is wrong.
If this were my unit I would try several basic technique variations (dense vs. light pack, playing with draw speed, pre-heating before hits etc) and give it a few more days or another week. (You might even wanna try a newer battery...ask FF to send you one since they stuck you with the old battery.) If you are still unhappy, tell FF and send it back. There shouldn't be any hassle for you, other than being without it for a few days (which, yes, is a hassle.
). But if you aren't happy with the way it's working, you should let FF fix it one way or another. Good luck and let us know what happens.