how is the iphone 6 plus battery life on medium to heavy usage ?

Nobody here can answer that, as everyones definition of medium to heavy usage is relative to their opinion.

kabillannash wrote:

HOW IS THE IPHONE 6 PLUS BATTERY LIFE ON MEDIUM TO HEAVY USAGE ?

No idea what that means - heavy call usage? heavy text usage? Lots of email? tons of gaming time? Streaming videos? Watching movies? Connecting other devices as a hotspot? Navigation map use? Photography or video? Music with Bluetooth headphones or but speakers?

People use their iPhones in an huge variety of ways, so your terms "medium" or "heavy" usage are meaningless without detailed specifics.