I haven't had any problems with the iPhone 4 battery so far (I managed to make it last 38 hours once), but in case you were wondering if there was a way to use solar power to get more battery life - well, here it is.
The Frostfire Mooncharge Hybrid Solar Battery Case For iPhone 4 gives your device 5 extra minutes of calling or 50 minutes of stand-by mode with 20 minutes of direct sunlight, but if you charge the battery inside the case via USB you get 5 additional hours of calling. So, not really powerful when it comes to solar charging - not unless you leave the phone in direct sunlight for a couple of hours.
Technical Specifications for iPhone 4
Improved performance for iPhone 4
- Stand-by: up to 315 extra hours
- Talk time: up to 5 extra hours
- Internet: up to 8 extra hours
- Audio play: up to 27 extra hours
- Video play: up to 10 extra hours
- Revolutionary solar panel technology allows your iPhone to charge from the power of the sun.
- Strong, light and attractive case design with built-in 2400mAh battery.
- USB connection allows you to charge or sync with iTunes without ever having to take your iPhone out of the case.
- Clean, green energy source allowing you protect and charge your iPhone anywhere.
- Comfortable, ergonomic design with a soft touch, non-slip finish
- Charge your iPhone while on the beach, camping, running, walking, hiking, or biking or travelling.
- Full access to your iPhone screen.
- Compatible with iPhone 4. Connection works with iPod for charging, although case is not snug with iPods
- LED indicator lights let you know the amount of power left.
- Impact resistant case
- This is a Li-ion rechargeable battery and therefore it takes 3-4 full charges before optimum capacity is reached
- Recommended to initially fully charge via USB