1. TRIANIUM ATOMIC BATTERY CASE FOR IPHONE 6 ($60)
This is a top seller on Amazon, where it averages 4.5 stars. The 3,100 mAh battery can completely recharge the 4.7-inch iPhone 6 (and then some). Put another way, it delivers an extra 10-plus hours of web surfing. The protective design has a very slim profile and a hard-shell back with indicator lights to show how much power remains.
2. LEPOW PIE IPHONE 6 BATTERY CASE ($60)
This product combines a regular skin for the 4.7-inch iPhone 6 and a separate 3,000 mAh battery, which attaches magnetically to the back of the case. Give the device a shake, and LED lights appear to indicate the power level. The case is a 4.4-star earner on Amazon and certified by Apple under the MFi Program.
3. EASYACC IPHONE 5/5S/5C EXTENDED BATTERY CASE (STARTING AT $28)
Users of older iPhone models are in luck, because accessory prices are lower now that the iPhone 6 is circulating. This Apple-certified case fits the iPhone 5, 5S, and 5C. It has won 4 stars on Amazon and comes in a variety of colors. The 2,200 mAh battery offers a 100 percent recharge.
4. MAXBOOST ATOMIC S PROTECTIVE BATTERY CASE FOR IPHONE 5/5S ($40)
This MFi-certified case has accrued an impressive 4.3-star rating and more than 2,000 reviews on Amazon. With 2,400 mAh, it more than fully charges an iPhone 5 or 5S. The case is available in a range of color combinations.
5. ANKER 7500MAH EXTENDED BATTERY COMBO FOR SAMSUNG GALAXY S5 ($40)
This is one of a few well-regarded Android battery cases. It enjoys a 4.4-star rating on Amazon and offers more juice than most other cases -- enough to triple the battery life of the Galaxy S5. The battery and protective TPU cover add considerable bulk to the phone, reviewers note.
6. MOPHIE JUICE PACK FOR HTC ONE ($50)
With the HTC One M8 out now, this case designed for the M7 is 50 percent off on clearance at Best Buy. It makes the phone much heftier, but a 2,500 mAh battery doubles the length of time users can go between charges. LED lights on the back indicate the status.