first i looked at a pic of where the battery is situated and then cut a smaller square central to the battery in the plastic back with a dremel and cut off wheel, only going 2mm deep or so till i could see a hint of shiny metal (battery)
i cut this square completely off exposing part of the battery.
then i slowly increased the size of the hole.
for some reason i have developed decent hand eye coordination and can actually cut fingernails with a stihl saw. so a dremel is fairly easy for me to hold still.
once the battery was fully exposed i started scraping out the grey epoxy with a tiny jewellers screwdriver.
the terminal was firmly attached to the back of the battery and i had to very carefully prize it off the battery using the same very thin screwdriver.
once this was undone the battery could be removed.
and another simply popped in. except it didnt work.
the other terminal needed to be scraped clean of a kind of laquer that was hampering a good contact. i didnt realise the laquer was there until i got my jewellers eyepiece out and had a look.
then i just cut a clear bit of plastic and drilled 4 tiny holes for the 2mm self tapping screws and a larger hole for the blue reset button.
i suppose what helped me is that i started messing about changing cracked iphone screens a few years ago and its the same type of care and restraint and PATIENCE!!! that is required.
apparently the resistance of the thermistor is 10k at 25 degrees c.
so i should be able to plot a graph and work out what resistance the trail tech sensor is.
unless someone can test theirs at 25 deg c?