What is this lead doing from the bottom of the cells?

Connects just under the terminal marked (C) on top of the chip.

Here are the Positive and Negative connections.

The 3/4 terminals connect to the camera... + - and temperature sensor. (c) is unknown to me, does it mean check?
Only + - connect to the charger, so i'm sure of the use of the 4th terminal, but for testing purposes?

I want to change to larger capacity 7.4V cells, but am unsure what to do with the third lead connecting to the circuit only marked BM (it looks like).
(I don't read a voltage off it, but would I read a current if it was running in the camera?)



Thanks

 

Additional info:

Volt meter reads 7.94 V from top terminals + and -

... reads 3.95V with - terminal and + taken from the connector pictured in image 1.

and the connector joins the circuit just under ther terminal + not (c) <--- sorry for misleading info

 

If it measures half of the battery voltage, it must be a connection to the cells that are in series, for charge monitoring.

 

If it measures half of the battery voltage, it must be a connection to the cells that are in series, for charge monitoring.

The voltages sound like lithium - a connection between cells for balancing is a given.