The units of electricity required will depend on source current/voltage, charging time, and specifications of the charger. Moreover, we would suggest you get in touch with the authorized dealership as they will be better persons to assist you in this concern.
It would not be possible to install an additional battery in order to extend the range of the Tata Tigor EV. The Tigor EV now uses a 21.5kWh powertrain that drives a 72V 3-phase AC induction motor. According to ARAI, the Tigor EV has a range of 213km compared to the 142km before. The increased range of the Tigor EV is due to the 21.5kWh battery pack, compared to the 16.2kWh battery pack offered before.