The first thing you should do is make sure that Windows 98's power-management features are on. Power settings tell the computer how long to wait after you've stopped working before shutting down resource-intensive programs.
Some people work continuously and then stop for a long time.
If that's you, set shorter suspend times. Other people pause a lot while they work, which makes short suspend times annoying as the machine shuts down just as they want to type again. Drain your batteries periodically to make sure you get a full charge life. To do this, leave the computer running until it dies. Then leave the computer running on a CPU-intensive task, like an OpenGL screen saver.