If you have an iPhone 4, Groupon has a nice deal you may want to check out today. You can get the Unu Battery Case for iPhone 4 and 4S for just $49 + $3 shipping ($79.95 List Price).
The UNU Battery case allows for an additional six hours of web surfing or talk time, 30 hours of music playback, or 240 hours of standby. The case also allows for full functionality, while its rugged bumpers protect your phone from nicks and scratches. Plus, the included slim back plate replaces the battery panel when you don’t need that additional battery life.
If you travel a lot or are just on the go all the time, this case is a great deal…especially if you are not always able to charge your phone before you run low on power!