The EN-EL14 battery can be used in the following cameras:
The insides of battery looks like this
|P+||Power + (Vcc)|
|S||??? (not used by battery)|
The battery is rated to 7.4V, but it shows +8.33V fresh loaded. After usage if voltage goes down to +7.30V it is pulled down to 0V by battery internal electronic (protection against deep discharge).
It was observed that T is not connected on D3100/D5100 and is only used by Nikon charger for protection against overheat.
The level of battery loading is shown by cameras based on measuring battery voltage (known starts from EN-EL3e).