What advantages did Britain have over Germany in the Battle of Britain?

The main
advantage that Britain had over Germany in this battle was the fact that it was fighting a
defensive battle and therefore would have an easier time being victorious.

One aspect of this was the fact that British airplanes were fighting over their own
home territory.  They could spend a long time in combat without having to expend fuel getting to
and from the combat area.  Their ability to get quickly to the combat area was helped along by
their radar stations operating on the coasts.  This allowed them to be more effective in defense
than the Germans were on offense.

The other major aspect of this is the fact
that Britain "only" needed to prevent Germany from destroying its air force and its
factories.  The Germans needed to gain a decisive victory so that they could invade Britain. 
The British could "win" so long as they did not lose badly.  A draw was good enough,
so was a close loss.

These two factors were the major tangible advantages
that the British had over the Germans.