Ok I am what I consider a iPhone power user, my phones is on 7X24 365 days a year. So I have always used some form of battery case. I have used 4 on my current iPhone5:
One I purchased when I was staying at a hotel in Las Vegas at a booth in the hotel's shopping area working on a project (un named brand) it is a 2000mAh battery with a cool little kick stand. Cost was $150.00. It has served me well. I go through at least 2 batteries per day. The re-charge time is about 6 hours.
Next comes the Mophie case that I paid about $85.00 for at a best buy machine at an airport I was passing through, the juice pack has been great as well but lasts half as long and still takes 4 hours to recharge. I have been a Mophie fan for years on IOS devices. Mophie.com
Next comes a Juice Pack Plus (trademark for Mophie or so I thought) that I purchased via ebay from proudparents2005. This was a horrible idea. The unit was defective out of the box and the seller would not replace it. Told me is was my iPhone 5 that was the issue because they never have had a unit fail. the included instructions did not match the unit I was shipped. I tested the unit on 2 iPhone 5's and it did not work on either one. they battery case was so tight on the iPhone 5 you could barely remove the case without damaging the iPhone itself. I just ate the cost of $35.00 and moved on.
In my search fro the perfect battery case I found a product from iBattz that is just great for me. it is the Mojo Refuel Removable Battery case, that is right you can actually change the batteries in the case, they use the i9300 3.7v 2200mAh Li-ion battery. I got 2 i9300's with the case, plus I bought a 3rd one. So far this has been the best solution! the case comes with a red or silver side bezel, usb charging cable, headset extension cable for plugging in you headphones to the iPhone5 ( I bought an extra cable for like $11.00 just in case I lose one). the instructions are dead on simple. I even sprung for an external battery charging device that I can plugin to recharge the batteries once I swap them our of the ReFuel case. The basic cost is about $90.00.
What you want your own iBattz gear click the link below.. Also their customer support is excellent!
So once again this is just what I have found works for me. Your mileage may very. I am going to be putting video on youtube on how I am doing with the Mojo ReFuel case. I have been using my iBattz for over a year now I have 5 i9300 batteries. I still love it. I have had to replace the back cover and that's is it.