Is consumption (in Ampere) calculated by the input or output rate?

Question

I have a notebook 12DC to 19.5DC adapter and I would like to know it´s consumption to find out how big of a battery I need. It says:

- Input DC 11-16V (8 A)

- Output 19.5V (3.34A)

Which of the two should I use to calculate how much this notebook´s consumption?

Answer 1

Your notebook is fed by 19.5V at up to 3.34A.

Therefore its consumption, at 19.5V, is up to 3.34 amperes.  

I would have thought that the machine has provision to function from its own internal battery which will be suitably rated.  

Answer 2

Consumption is in Power (Watts or Volt Amperes).

Power is Amp.s x Volts. Either without the other is just

a characterisitic of the power being delivered.

Your device supplies  65.13 W. maximum.

(Some of the input is lost to heat.)