Put the thermistor in the middle of the pack,
preferably sandwiched between two cells.
It will be chance, anyway - the worst/best
cell will seldom be right in the middle, anyway.
A 40v terminal voltage is not unusual for a
severely depleted or damaged battery pack
with 16 cells, but it certainly should not be
at 1A at this voltage. If your cells are the
"fast charge" type, they can be charged at
C/1 (i.e., 1.6A), otherwise the maximum
rate is C/10 (0.16A).
If it is not too difficult to get to the internal
cell connections, you will have better results
charging fewer cells in series (2 to 6).
16 cells is an unusual pack (19.2v). Are you
sure that the charger has this in its range?
As for soldering the cells, use a soldering gun,
preferably a 250W or so. Tin the cell ends
and the tabs first, then solder them together.
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