OP here. In the meantime, I've tried leaving the battery + charger in the unit for basically a full day, as well as left the battery out overnight. I think the battery itself is fine. While the unit was getting "repaired" by Nokia for this exact same problem, the battery was just sitting on my desk. When I got the unit back and popped the battery back in, it came right up with about 75% juice before it bricked again a few hours later. It's the original Nokia battery, original 128MB memory card, original Nokia USB cable, charger, etc. I didn't even install any software when it bricked this time, and obviously the OS update never started to touch anything on the device.

I've already paid shipping and waited a few weeks once to get this repaired, which obviously didn't work, I'm not looking forward to having to do this again, nor am I of the opinion that another repair cycle will actually do anything useful. I'll call Nokia again today since the holidays are over now and see if I can get a refund, or a new replacement unit if they won't do that. This one's just simply b0rked.

Sorry if I'm all grumpy in these forums, but it's pretty frustrating. I also think it's a good thing to communicate issues like this so that other people can see if what they're getting with their device matches others' experiences.