Not just battery, but...
GKrellM might be worth a look-see? It displays your CPU(s), processes, disk, eth0, ppp0, memory, swap, mail and, ooh-boy, battery status (and you can add fans and the like if you want). With an "invisible" theme, it'll sit there on your desktop off in a corner someplace and keep you apprised of what's going on.
It may already be on your system (open a terminal and enter
gkrellm and hit the return key) or it ought to be available from your distribution or, what the heck, at
http://members.dslextreme.com/users/...m/gkrellm.html.
Maybe that's too much, but what the heck.
Hope this helps some.