All iOS devices (and most smartphones) charge at 5 volts, the standard for USB devices. The difference between the iPhone and iPad adapters is the rated amperagethe iPad charger is rated to handle 2.1 amps, while the iPhone charger is rated for 1 amp. But the amperage rating is only a measure of the adapter's maximum capabilitythe actual amperage is determined by the load (i.e., the iPad or iPhone). According to Steve Sandler, founder and chief technical officer of AEi Systems, an electronics analysis company, modern battery-powered electronics have a lot of complexity between the charger and the battery, including battery-charging circuits within the device and battery-protection circuits in the lithium-ion battery itself. These circuits are designed to manage the flow of electricity to the battery, and if the circuits inside the iPhone were designed to tolerate 1 amp, but are routinely exposed to 2 amps, that could stress the system over time. "Even though you may not instantaneously say, 'Wow, I just destroyed my battery!' you may limit its life over the long term," Sandler says, "but you wouldn't know for a year or more." Our advice: Since Apple claims compatibility between the iPad charger and iPhone, pay for the extended two-year warranty for the iPhone to ride out your cell contract, and charge it however you like. If your battery degrades severely after the first year make Apple give you a new one.
Have a beautiful, warm almost-summer (tomorrow) day, Las Crucens!