Ah, it helps to discover that it’s actually a 6S rather than a 6.
It appears that I haven’t properly connected the battery back up, since the hard reset didn’t work. I did my best to connect the battery before adhering it to the battery spot, but the connector doesn’t seem to “click” or otherwise confirm that it is properly positioned. The left side of the connector (closest to the battery) seemed slightly raised, which made me wonder if I had done it correctly. So I’m probably going to have to try using my last adhesive strips to lay it in better to allow for a better connection. I’m also worried that I may have damaged the connection spot. Is there anywhere on here where this is discussed? This is my second battery replacement, but first on this particular phone, which is apparently a refurbished one (and which has a slightly different looking connector cover).