It depends upon which panel you are using, but, in any case, there are generally a multitude of choices. If you have fbpanel, or if your panel allows genmon plugins, look at http://lxlinux.com/fbpanel.html
. If you have access to openbox dock (using openbox window manager), see http://lxlinux.com/dock.html
. In general, just do a web search for "Linux panel battery indicators".