The iPhone Battery Voltage. The iPhone uses a lithium ion polymer battery. The battery has a capacity of 1400mAh and 3.7 volts. The iPhone 4 offers up to 14 hours of talk time on 2G networks and 10 hours of Internet usage over a Wi-Fi connection. Its predecessor, the 3Gs, offered 12 hours of talk time on 2G and nine hours of Internet usage over Wi-Fi. Because of the iPhone's many functions and applications, these figures can vary quite a bit.