On my dv6625us, which is a Vista notebook (I understand that yours is XP, yes?) I can simply click on the battery icon in the taskbar tray to call up my battery options (and it is in my Control Panel as well)...and it is no different in my wife's Sony Vaio, which is a Windows XP machine...I am sure that it is easily accessed on your zx 5000 as well. Virtually all notebooks have an easy means to control how your computer runs under battery power.
It is always a trade-off between battery life, versus screen brightness, cpu speed, etc. Many/most laptops have some pre-set points you can choose, such as "max performance" or "max power savings" etc., and pretty much all of 'em allow you to create custom settings to your liking.