How long a tablet’s batteries will last away from a charging point or power source of some type is important, but it is a very difficult thing to measure. Battery usage is not constant, and there are many things that will drain the battery faster. Bluetooth and WiFi, if a tablet has them and they are switched on, increase power use. So do many games and watching videos. Reading ebooks tends to be a lower power activity, and general internet use is variable.
Under ideal conditions, the Tagital T7K‘s battery is assumed to last four hours, but more intensive usage will drain it faster. In standby, when it is not actually being used, the battery will last for weeks.
Four hours is not a particularly good battery life, especially as it could well be less. As such, if the tablet is being used whilst travelling, it would be a good idea to take along AC adapters for plugging it into the mains or car adapters for recharging it in a car.