As one of its daily deals, Caloby offers the uNu Power DX Plus 2,400mAh Rechargeable Battery Case for iPhone 4 and 4S in Black (pictured), Silver, or White for $27.99 with free shipping. That's $15 under our mention from a year ago and the lowest total price we've seen. (It's also a current low by $12.) It features an integrated LED power gauge and stores power for up to 10 hours of talk time and 9 hours of 3G web browsing (up to 14 hours on WiFi). Deal ends today.