If you get this error on your laptop it means one of two things
1. Your battery is dying, and it needs to be replaced
2. Windows 7 cannot properly detect how much power is in the battery
To determine what's wrong,
click start
In the box that says "search programs and files", Type in CMD
You should see a "cmd.exe" show up in the top of the start menu
Right click the cmd icon, run as administrator
type in powercfg -energy
This will test your battery, and produce a report in C:\Windows\System32\energy-report.html
You can open this file in a regular browser or Word
If it is able to read the battery, and produce a report, look at the line that says "design capacity" and "last full charge"
This will show how much the battery should hold, and how much it's actually holding
If you run the test over a few days or weeks, and this number is steadily decreasing over time, it means your battery is dying, and you need a new one eventually
You can always untick the "warn me if my battery needs replacing" if you just want to get rid of the annoying message
If it is unable to read the battery and produce a report, then windows is not communicating with the battery.
This is a BIOS issue, and it means that Windows 7 just isn't going to read your battery properly.
You can try updating your BIOS, but it probably won't work.
Long story short, there's nothing you can do about the warning.
in your cmd box, run powercfg -setdcvalueindex SCHEME_CURRENT SUB_BATTERY BATACTIONCRIT 0
This will just let windows run until the battery hits 0, regardless of how much power it "thinks" it has