Unusually low in power capacity for an iPhone 5 battery case, Ventev's new Powercase 1500 ($80) promises "up to an additional 6 hours of talk time for the iPhone 5," using a 1500mAh cell. Sold solely in the gray color shown here, Powercase 1500 notably has a slimmed bottom design to provide easier access to the headphone port and speaker than other battery cases. Power is supplied at 1 Amp, and recharging of the battery also takes place at that speed,…