This well illustrated modification instruction set by Jamie M. allows you to run your WRT54G router without external power supply. You may think the trick is in somehow squeezing a battery pack inside. It's much better. A simple modification inside the router implements Power Over Ethernet (POE). You can power the router through the CAT5 cable.
Code:
http://www.linksysinfo.org/forums/showthread.php?t=54169
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