I always plug my laptop into a wall outlet using an extension cord because the laptop's battery is so old it's dead. More than once I have put the plug from the computer cord into the plug from the extension cord so that only 2 of the 3 prongs were in the holes in the extension cord plug. Pretty-soon I get a message on my computer screen telling me I should plug in because my battery was low! It always takes me a minute to figure out what's wrong.