I bought this. It was $24.99 when I bought it a couple of weeks ago and is now down to $19.99. The charger works fine and the batteries last just as long as the one that came with the phone from Sammy:

Amazon.com: Onite 2x 2600mAh Extended Li-ion Battery for Samsung Galaxy S IV / S4 I9500, with Charger: Cell Phones & Accessories

 

Register your phone at Samsung's website, they will then email you a 50 percent off coupon, and you can order the charge and battery there.

 

There is a official Samsung one, and I've seen less expensive ones on Amazon by reliable companies like Anker who make stock size batteries with external chargers.

 

Wireless charger is the way to go..... bought 2 actually.....but what is wonderful is letting the phone rest on the pad all day at work at then it is fully charged when I leave. The back and two charges was very very reasonable with my 50% off Sammy gift for registering.