I have a Toshiba Satellite pro a300 laptop with windows xp its about 4 years old. I just got a new battery because the one I've had since I got it wasn't lasting more than twenty minutes. I put the battery in and turned on the computer and changed the settings as the insturctions told me to. I changed power scheme to toshiba power saver. But when I look in power meter it says unknown remaining. So when its unplugged or when its charging I've got no idea what percentage it is at. I tried unplugging it, taking battery out and holding down the power on/off button for 16 seconds. I put battery in again and turned on. But it still says unknown. Please can you help? Thanks

A new battery can take some time to be properly recognised by the OS, especially XP as it is now 12 years old.
Make sure you are fully updated and patched..