Battery Question?

I know this is most likely a major noob question but i don't know how else to search for it. This is a 3.7 volt cell phone battery but there's three connections. Positive, Negative of course, and then another I'm not totally sure of, is it a ground?
Picture included
Thanks

Alot of batteries are "smart" these days, that terminal is probably a temperature sensor so the device can know to shut off charging when it gets to a certain temperature. You can check by measuring the resistance from the middle pin to the "-" ground pin. then while still measuring, or coming back later sit on the battery or warm it up with a bit with hair dryer or heat gun and check again, probably show a good change in resistance. If it does not change, its possible that pin is used to somehow balance the charging to the individual cells in the battery, not sure how to verify this though...

A 3.7V Lithium battery only has a single cell so it does not need multiple cells to be balanced.
The thermistor connected to the second terminal is normally not used for charging. It tells a defective charger to shut off when the battery gets too hot even if it is not fully charged.

test 'em using LEDs if you wanna be sure. I built battery packs out of 'em.