"Mr Macaw" wrote in message news
I've seen inside drill batteries before (NiCad ones) and there's usually
just three terminals to the pack, -ve, +ve, and one for the temperature
sensor. But this one has a 4th pin, which is connected to the -ve of the
batteries via a 10K resistor. What is its purpose?

https://www.dropbox.com/s/1np3y4ubr4....jpg?dl=0&s=sl

Bottom left large pin is connected to -ve of cells and one end of the
temperature sensor (a little black blob) and one end of the 10K resistor.
Right large pin is connected to +ve of cells.
Top left large pin is connected to the other end of the temperature
sensor.
Small pin is connected to the other end of the 10K resistor.

I don't have access to the charger for this pack, I only bought this pack
to take the cells out to replace them in my own battery pack, as this one
was half the price.

If your battery pack doesn't have one - don't worry about it.