Inside a self-testing emergency exit sign.

This is quite neat. It was sent to me after it had reached the end of the battery pack's useful life. It's often cheaper just to replace a fixture than it is to find and replace a battery in these units. If you had a lot of identical units it would definitely make economic sense to get some spare battery packs though. Especially in non maintained fixtures where the LEDs didn't get a lot of run time, so were in good condition.

This unit is more complex than the typical emergency lights in that it does the routine runtime tests itself. I'm not sure the frequency of the tests is as important with LED fixtures as it used to be with the fluorescent ones. And technically speaking, a short weekly test on a traditional fluorescent version could age the tube badly over a few years with the number of cold starts.
The control system seems to test the LEDs by current draw and does a short weekly test and a full 3 hour duration yearly test. The requirement for these lights is to run for 3 hours continuously and then recharge fully within 24 hours.
If the light fails the self test it beeps and flashes a red light to warn that it has failed.

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