Battery Power Saver only has, in fact, two screens - both dialogs and both very well laid out, in a manner in which you can 'read' what the utility's being set up to do:
Nice. Of particular note here is the option to trigger the Symbian 'power saver' mode based on inactivity. The principal saving here is that 3G gets turned off while youre not actively using the handset and you're back on 2G data, which is something I often have to do manually, especially when travelling. So you get 3G when the screen's on, and then after a while this utility automatically drops you back to 2G, for background email etc without needing the higher speed and power drain.
Also of note are the optional audio notifications that get played for every 10% decrease in battery life. Plus quite a number of rules and a fairly detailed help dialog explaining the functions in more detail.
You can download Battery Power Saver for free here in the Nokia Store. Comments welcome - have you relied on this long term? Did it get in the way at all, in terms of disabling connectivity or features that you relied on having running all the time? Or was it a star power-saving utility? Either way, you can't beat the price and well worth a look.