Earth Terminal on Battery

I have converted an Ni-Cd 36v drill battery to an 18650 battery.

The connector to the drill has the obvious positive and negative terminals, but it also has an earth terminal.

This has a black wire going into a silver thing (red arrow below), then another black wire comes out and was soldered to the side of one of the NiCd Cells (Blue Arrow), Note this cell was the only one that had a space to solder this to.

I am wondering whether I need to keep this?

Whether it serves any purpose?

Whether with 18650's it is even safe to do this and if so on which cell within a 10s setup.

My understanding is that the metal side of 18650's are part of conductive negative electrode, so should this just be connected to negative terminal or even just cut?

This is a picture of it

That looks like the original temperature sensor.

I agree, if it was attached to the side of the battery it was a temp sensor

So should I ditch it or try to attach it to one of the 18650 cells?

Stick it between 2 cells.

Just be careful that it is note going to rub through the heatshrink and short out your pack.

If the 2 cells you place it between are parallel this won't be an issue but if they are series it can be.