A laptop battery monitor comes with Windows - at least it does with ME and 2000. I haven't checked with 98.
When you right-click on an open area of your desktop and left click on Properties you get to the screen setup dialogue.
Click on the Screen Saver tab at the top (Windows 2000) and then the "Power" button. You can select a preset power scheme for a laptop or create your own and on the "Advanced" sub-screen there is box for a check mark to "always show icon on taskbar".
Also available through Control Panel/Power Options.