[pip22]

A laptop has two batteries -- one large rechargeable one which allows the laptop to be used without mains power, and a small round internal one (called a CMOS battery) which maintains a constant small voltage to feed the CMOS chip. This chip contains all the information and settings for the laptop's vital components, a system known as the BIOS (Basic Input/Output System). When this battery dies, all that hardware info is lost so the laptop won't boot up.

If the error refers to the rechargeable battery, you should still be able use the laptop by plugging it into the power supply. If it works like that, the error probably means your rechargeable battery has reached the end of it's life -- they don't last forever.

If the error refers to the CMOS battery, you will need to get it replaced at a PC repair shop unless there is easy access to it underneath, because opening up a laptop can damage it if you don't know what you're doing.