Newbie to the forum here! I bought an inexpensive Roomba clone robot vacuum with the intention of pulling out the stock mainboard and replacing it with a bespoke controller. I am currently tearing down the bot and mapping all of the i/o. It has a 14.4v Ni-MH battery pack which has 3 connections: +ve, -ve and a 3rd unknown connection.
See Batt Con.jpg
This 3rd connection is picked up on the chassis, but isn't/wasn't wired to the mainboard. My guess is that it is for battery level monitoring, for recharge behaviour triggering, which the higher spec model of this range does feature, but my model does not.
I (very carefully) opened the battery pack when it was fully discharged and traced this mysterious connection to a component which looks like a tantalum capacitor or thermistor (the other side attaches to the battery +ve) and I have no idea what this is or what it does beyond my guess! See Hmmm.jpg
Hopefully someone can help me!