You may also want to consider getting a Hyperion or zerolemon battery. Those are the two big names in extended batteries, and they are built to last.
Zerolemon makes ultra sized batteries, there's people here that have their 7200 mah batt for the s3 and it last for on average around 4-7 days depending on use.
Just so you know though, once you reach the 6000 mah threshold, the stock Samsung charger won't be able to charge it effectively so you would have to wait around 6-10 hours for a full charge. Just charge your phone overnight and you'll be fine.
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