Laptop Clock Was Wrong, and Now It Powers On to a Black Screen

Before assuming it’s the CMOS battery, disconnect the charger and the laptop’s main battery if you can, then hold the power button for 30–60 seconds. After that, connect only the charger and try starting it again. On many laptops, the internal battery is accessible from the bottom panel, but you’ll need the correct screwdriver.

For a Lenovo Legion, look up the exact model’s hardware maintenance guide before opening it. Some models use a small cable-connected CMOS battery rather than a simple coin cell, and replacing it may require removing the bottom cover. Don’t buy parts based only on the incorrect clock—the black-screen problem may be unrelated.

The $150 quote might be fair, but it depends entirely on what the shop believes is faulty. A CMOS battery replacement is usually inexpensive, while diagnosing a black screen or repairing the motherboard can cost much more. Since the laptop has not been inspected yet, ask them what specific repair the quote covers before approving it.

A dead CMOS battery can cause the clock to reset, but it normally won’t prevent a laptop from powering on when the charger is connected. Since yours powers on but shows a black screen, the issue could be with the display, memory, graphics hardware, or a failed boot. Check whether an external monitor works and whether you can see anything on the screen with a flashlight.