The power supply of the Tobii Dynavox T-Series (for the device models T7, T10, T15) operates at 12 Volt with a maximum of 3 Ampere. This means the power supply will provide a maximum of 36 Watt which corresponds to 36Wh maximum power consumption. The exact power consumption is very dependent on the use case, the screen brightness, etc. but in normal use the device will consume much less power than that. As a comparison, a regular LED flat screen TV can consume around 130 Wh.
In internal stress tests with fully charged batteries, screen brightness set to 100% and WLAN and Bluetooth turned on, did the T15 run approximately 6 hours +/- 10 minutes on one battery charge. In normal use, batteries last much longer, usually about 10 hours.
To charge completely, empty batteries takes usually 4 hours or longer.