All emergency fittings should be regularly tested, they are normally installed with a test switch near by, which can only be operated by a special key.  Each fitting should be inspected daily to check that the LED is on.  Tested monthly to see they operate, and every 6 months they should be run for an hour.  Every 3 years a full 3 hour duration test should be carried out, preferably until the batteries are run down completely.  In this way the batteries which are sealed Nickel Cadmium can maintain a full charge, if you only partially discharge them they develop a "memory" and only part of their power is available.  All emergency fittings should have a red LED, which shows that the batteries are charged and ready for action, if the LED is not lit the batteries may require replacement.