The battery on this Sharp Mobilon HC-4500 is completely dead. Time to rebuild it!
Don’t solder to batteries, there, I said it.
I don’t think I’m going to end up getting the custom serial cable for this thing, so if I ever want to make it do anything fun I’m going to have to get IR finally working or find out if there is some kind modem to LAN adapter. Then I could get this on a network with another computer to transfer files.