Brendan,
My understanding is that the Brunswick Oels Regiment in British service operated as Light Infantry, and Prussian Light Infantry operated in two ranks anyway. When they joined the 7th Division that Division was initially primarily acting as a second “Light Division” although that role faded later. Wellington’s tactical concept was for Brigades to converge their various battalion light companies to form small temporary light battalions, which then provided a skirmisher screen for the Brigade (see my article about this here):
In other words skirmishers were a Brigade asset and there was normally no need for battalions to form a replacement temporary light company. The only reason I could think of for a battalion to still need it’s own skirmishers would be in the unusual event of a battalion being temporarily detached to an independent role during a battle.
Rod