What are the Best External Battery Cases for iPhone 4s?

You mean an external charger?

This one is very great.http://www.amazon.com/RAVPower-Dynamo-On--RP-PB03-External-Flashlight/dp/B007HUTXV8/ref=sr_1_2?ie=UTF8&qid=1341824138&sr=8-2&keywords=RAVPoWER

I think that they are cases that double as extra batteries.

I hadn't heard of that, but you might check with Joe Nation. He gave me good advice on phone cases.

Looks interesting, but I am really looking for the battery/case combo. Thanks for the idea, though!

I personally use 1900mah rechargeable external battery for my iPhone 4 but i found one new on Amazon 'New Trent iCarrier 12000mAh' and it is the most popular pack around. The other are Satechi iCel 4800 mAh which works as battery extender and charger, YooBao 4800mAh which come in packs for all kind of smart phones and Solar Power Juice Pack for iPhone 4s.

I ended up getting an external Mophiethat you attach only when needed. I was not to happy with having to add more weight to the phone.

Also, this is very funny. I had a car charger that I bought with my first computer, ca. 1998. It had this square connection. When I bought my 2nd computer, I needed to add an extension that had a USB port. Now I found, that for 8 bucks, I could get an extension , usb to 30 pin Apple attachment.

I wonder what that car charger will look like in 20 years, (if I live that long!)

External battery life for iPhone 4/4S (All Models)
High capacity 1700 mAH battery hidden inside ultra thin durable case
Sync & Charge simultaneously
Slim fitting and nearly weightless design minimizes any added bulk
Boosts cell reception for iPhone 4