Can anyone describe what is your "heavy" usage?
I still have to charge my phone every night for what I'd describe as normal usage. With heavy usage I need another quick charge in the evening. Maybe I just use my phone more than most people.
I can get away with two days for light usage, that is barely touching my phone apart for some IMs and browsing.
Are you using your iPhone with the brightness jacked up? Facebook/Twitter/LI or social aggregators including G+? Social, push mail, crappy radio (LTE) signal (even if using wifi but keeping cell signal 'live'), your preference of brightness &/or conditions you're using your iPhone in will each contribute to its 'life' during the day...
...as well as what you're up to. If you're shooting and editing video, playing intense games, down/uploading intensively...battery life will defitiely get eaten quicker. iCloud and Dropbox. GDrive/1Drive syncing if you're using them also run in the background pending the limitations you're giving it
But the big one I've found, again...regardless if using or being in a wifi environment or using LTE (or not using the signal, just a low signal with constant hunting for signal) to be a HUGE contributor to life expectancy throughout my day
That said, I've had mine since November second and I've NEVER run out of 'juice' ...even during long Days of Heli Skiing, twenty hours with 18 in the 'chill', I'm still at 20-40% by the end of the day ...and I've shot 20GB of video
It would still extend the battery life.
And the weight. And the size. And (extend its) lack of aesthetic appeal & ease of use ...and I'm a HUGE Mophie fan. Had one on almost every iPhone since the '4'. Doubling the weight and adding to the length, Eliminating its looks and its incredible form factor when unnecessary (there's Mophie 'packs' that would be cheaper, with more energy and not necessary to holster to the phone that are more convenient if you're away from 110 for an extended duration) is silly
Has Mophie even MADE an iPhone 6+ case?
I've got both the Note 4 (primarily a business/family run line) and the 6+. I've owned em all (iPhones) and a ½ dozen Androids, each iPad as well (again, instrumental and game changing with our business, both platforms) and I've never been as happy with battery life, performance, 'package', form factor and 'display quality' than I've been with the 6+, the Note 4 is pretty damn close (as far as energy) but the 6+'s 'performance' with apps in parity is Always a more 'fluent' and enjoyable experience
Just MHO
J