Sanwa Supply has something to help you download and play with all those apps as your iPhone's non-swappable battery runs out of juice. The "400-BT001" is a JPY4980, 50-g  lithium-ion polymer battery that recharges via your PC's USB port and then powers your iPhone via its dock connector. Powered up, the device will grant you another 3.5 hours of talking time, 7 hours of video watching, or 36 hours of audio listening.
http://direct.sanwa.co.jp/ItemPage/400-BT001 (Japanese)