found some more information
According to Marine Rundschau 1983/3:
"Canopus-battery 2 15.2 cm guns from HMS CANOPUS since 1938 400 m. SW todays Port Stanley airfield".
They are wrong about guns being former HMS CANOPUS ones, they were former HMS LANCASTER guns.
The old battleship HMS CANOPUS was guardship in the Falklands during 1914, she was inside the
harbour and had at least one observation post on dry ground. This is the spot were the guns are named: "Canopus hut". So maybe that's the reason MR writes they were former HMS CANOPUS guns.
So it seems the second gun was also moved from Sapper Hill to the place Canopus hut.
There is also a photo taken during WW2 in the same MR with the guns firing a salvo.
Nuyt, try again on Google Earth.