Got the iphone 4s battery charger case using the groupon deal.
Pretty sleek and very good finish. The only complaint i have about the case is that the phone's screen protrudes, so doesnt provide complete protection if you place your phone screen-down on a surface.
Haven't tried a full run-down of the phone battery and charge with the case, yet.
It gets heated when the case charges the phone, and by 20% increase in charge, it reaches its peak "hotness".
I usually charge my iphone through a PC/laptop, so i hope this shouldnt be different in terms of amps supplied.
But i'm still worried due to the reasons mentioned above.
So i've decided to use it for long days, when i might have to travel, rather than a daily-use charger.