If you have a laptop/netbook, rather than add the KDE4 battery monitor as a widget, you can include it in the system tray. You can also get rid of the widget for Device Notifier and add it in the System Tray, you can set it so it will only take space when needed. There is also a weather applet hidden there.
After first ensuring that widgets are unlocked, right click on the "i" at the right of the system tray, and then select "System Tray Settings".
On the "Plasma Widgets" setting, you can add a choice of widgets right there in the system tray. On the auto-hide settings, you can decide which of the icons are permanently displayed, and which are only displayed when needed. You can also set the "System Notifications" so they stay up until finished, I know that someone wanted this enabled for copying actions. You can be selective about which system notifications are actually displayed, that's on the "Information" tab.
Plenty there to be playing with....