[antipole]

Screen brightness can be set in the Energy SAver control panel. By default, the screen is dimmed slightly when on battery as a power-economy measure. If you want to keep the bright screen when on battery power, go to the Energey Saver control panel, select settings for battery and the Options tab and then unselect the 'Slightly dim the display using this power source'. Voila! But yes, your battery charge will not last so long.

And yes, my reasons for getting a DC charger were to avoid the inefficiencies of an inverter on a yacht, where I only rarely run the engine.