Well I believe Amzer makes add on battery packs powered by either a single or two AA batteries. Other than that, here's some general battery life suggestions:
1) Reduce number of homescreens
2) Turn off wifi and 3G when not using them
3) Turn off hepatic feedback and keytones
4) Reduce number of widgets, especially ones that use a live data feed (constant updating)
5) Turn screen brightness down
6) Don't use a live wallpaper, use a picture with dark colors
7) Are you overclocking? Lower the CPU max if you are.
8) Underclock the CPU min.
9) Experiment with different governor/io combinations. The best yielding
in my testing were Interactive/sio and SmartassV2/cfq.
10) Try undervolting a bit. Apps like Incredicontrol or System Tuner work, but
be careful. In my testing this ROM was only stable at decreasing all
values by 50 mV.