Missing Battery Icon on System Tray

Hi,
I have a Sony Vaio laptop running Windows XP Home Professional Service Pack 3. My problem is, the battery icon on the system tray sometimes disappears without any error message. I go to Power Option Properties then checked the always show icons on the taskbar. But it still happens more often now.
While I was searching for a solution on how to fix it, I accidentally deleted the Microsoft ACPI Compliant Method Battery Driver from my device manager. Since then, I cannot be able to use my laptop without using the charger adapter. I cannot run my laptop on battery power anymore.
And the battery icon on my system tray is not showing up permanently. I don't know what to do with it as I searched on hundreds of forums, but could not resolve the issue. I don't have a restore points to go back to my previous settings. Even on safe mode, the battery icon is not showing.
Does anyone know where to download the driver for this?
Or if there is another resolution on how I can be able to fix this, please send me some advice. I don't have any disk with me, but I also want to know if I can provide a disk and recover or reformat my laptop, will I be able to run my computer again with battery?
Please help.
