Your laptop is plugged in, the charger light is on — so why is it running at a crawl? The answer isn't Windows, it isn't your drivers, and it probably isn't your charger. It's your battery. In this deep dive I explain the full signal chain from a failing battery all the way to a throttled CPU, why this happens before the operating system even loads, which Lenovo, HP, Dell and Acer models are well known for it, and what a proper board-level diagnosis actually looks like.