If having extreme battery life is more important to you than having a phone that fits comfortably in your pocket, Mophie has you covered. It produces extended battery cases for phones that make them monstrously huge, and the G4 Juice Pack is on sale for $10 in AT&T stores. That's down from $100.
This is clearly an inventory clearing thing with the G5 on the way in a few weeks. The battery pack is already sold out online, but it's in plenty of AT&T stores. There are at least half a dozen around me that have it available. So yes, you'll have to leave your cave to pick up this massive battery.
The Mophie Juice Pack includes a 3400mAh extended battery for the G4. With the stock battery, that's 6400mAh. It makes the phone obscenely thick, but you can't have everything. The same case is on Amazon, but the price has only dropped to $50 from the $100 MSRP, so the AT&T deal is still solid.