Running a laptop charger from an inverter is asking for trouble. You lose a lot of power (perhaps 25% or more) converting from 12v DC to 230v AC and as much again going back down from 240v AC to 19v DC or whatever the laptop needs.
To get a typical 65 watts into the laptop, you are putting 87 watts into the adapter.
To get 87 watts into the adapter, you are putting 116 watts into the inverter.
To get 116 watts into the inverter, you are drawing 9.6 amps out of the battery.
A sustained 9.6 amp load will reduce the voltage into the inverter.
With a low voltage input, the inverter's output voltage may drop from the nominal 230 watts to something like 215 volts, which will upset a power supply designed for 240 volts input.
You can easily tell how much power is being wasted: it is the heat coming off the inverter and the power supply adapter.
A MUCH better approach is to use a proper 12v adapter for your laptop.
They are usually no more than about £20 and are about 95% efficient. So that 65 watts output is only costing 5.7 amps of battery power.