How many minutes does a 45mah battery last?
That completely depends on how much current is used by the
circuit or device that's
connected to the battery. For example, if there is no circuit or
device connected to
the battery, and no current is used, then the battery lasts for
quite a long time.
But if you lay a screwdriver across the battery terminals and
create great balls
of fire, then the charge on the battery may only last for 1/2
second.