According to the Taipei newspaper, "Apple has reportedly placed its next-generation iPhone battery orders with only two suppliers: Taiwan-based Simplo Technology and China-based Shenzhen Desay Battery Technology. Dynapack, a battery supplier for the iPhone 5 and 5c currently has no orders confirmed, according to sources from the upstream supply chain."
This is about the right time for Apple to ramp up orders for the next generation iPhone 6, so the report has some credibility. UBS analyst Steve Milunovich, in his checks with the supply chain thinks that we'll see the iPhone 6 in August or September.
Not much else is known about the iPhone 6. Some rumor reports suggest that the new iPhone will have temperature, humidity and pressure sensors.
Other rumors suggest a larger display with a much thinner bezel.
These are all just rumors. For the facts, Erica Sadun over at TUAW, has posted a helpful article: "EVERYTHING we know about the iPhone 6."
iPhone 6 concept via Martin Hajek.