If the sleep light flashes on Mac
If your computer has a sleep indicator light, it’s normal for it to slowly pulse (brighten and dim) when your computer is in sleep. If the sleep indicator light flashes (turns completely on and off repeatedly), the computer may need service.
If you hear beeps during startup
If you hear beeps when your Mac starts up (the beeps are different from the startup sound some Mac computers play) and the sleep indicator light flashes, your Mac might need service.
If the sleep indicator light flashes during startup
If you don’t hear beeps, but the sleep indicator light flashes five times when you start up your Mac or wake it from sleep, your Mac might need service. See Find how to service or repair your Mac.
Important: If your Mac has a faulty battery, or no battery, and it runs out of power, you could lose unsaved changes. To avoid this, keep your battery charged.
You can continue using your Mac before it’s serviced. Use a different battery, or connect the power adapter and plug it into a power source.