I just quickly watched your video and while I'll watch again sometime this weekend, I'll only point out some quick things. It is 2:11 am here.
1) I always measure a battery before using it even if it is supposedly new. That way, I avoid surprises.
2) The RS232 icon appearance/setting seems inconsistent. When you changed to the Duracell batteries, it was clearly on. Then when you did the off "side to side" off and back on, the RS232 icon was off. After the disassembly to see the insides, the RS232 came back on.
3) Okay, I found the manual, software, datasheet, etc
http://www.multimeterwarehouse.com/TP4000ZCf.htmThe website says it takes a 9V which is clearly wrong.
4) For the software part, I suspect you may find bugs and getting the proper driver to work a bit of a challenge as some of the reviews on Amazon. I recommend you install it on a PC that doesn't have all your important data so if the install screws up, you are not sol. Hopefully, you will read this post before doing the install.