

http://www.digitaltrends.com/cell-phone-reviews/samsung-galaxy-s6-review/
The battery is really the key to the Galaxy S6. If it whittles down quickly, the phone’s features and performance hold less credence. The Galaxy S6 actually has a smaller battery (2,550mAh) than the GS5 (2,800mAh), but it’s supposed to use a more efficient processor. The jury’s still out on the Exynos chip, but questioning the longevity of the non-removable battery is totally understandable.
Samsung flatly noted that it only went with the non-removable design because it was confident the battery could stand up on its own. Well, that confidence has a backup plan, just in case. The Quick Charger that comes in the box with the phone can give you four hours of use (or two hours of HD streaming) from a fast 10-minute charge. Samsung says it can charge from empty to full in only 80 minutes. I wasn’t provided with the proper charger, so I can’t verify that those numbers are indeed accurate.
The second part of that plan is wireless charging support for both the Qi and PMA (Power Matters Alliance) standards. This is the first smartphone to have dual compatibility, so it’s a big deal if you own a wireless charger. I tried to charge it on an old Powermat charger (which used PMA technology) but it didn’t work. It did work like a charm on a Qi pad, however.
Charging options aside, the battery’s overall performance didn’t impress me. I could go through a full day, except it drained faster than I expected. This isn’t to say that it’s awful and a major cause for concern, just that it isn’t as robust as it should be. In some respects, I consider the GS5 to last longer than this phone does.
This is when you wished Samsung went with a 1080p display. The 2K works better for above 5.5" and tablets.
I don't bother with AnandTech for reviews anymore. Only sometimes. LONG and well-written but you might as well watch a video from Android Authority and PocketNow TELLING and SHOWING you. The only knock from Josh Vergara and Michael Fisher is they never give you actual data on battery life. That's where GSM Arena and Phone Arena comes in with their ratings data.
Waiting for PA for further confirmation that the 2015 flagships have WORSE battery life than their 2014 predecessors. Phone Arena seems far more accurate with the real world SOT as their test seems more rigorous than other sites.
For further confirmation that 2K screens is useless or some of these OEM's should have went for a BIGGER battery since the SoC is going to be faster, check the LG G Flex 1 vs 2.


G Flex - Snapdragon 800 / 6" / 720p / 245ppi / 3500 mAh
G Flex2 - Snapdragon 810 / '5.5" / 1080p / 403ppi / 3000 mAh
Phone Arena
Samsung Galaxy S5 - 7 hrs and 38 min
HTC One M8 - 7 hrs and 12 min
LG G Flex - 7 hrs and 11 min
At least the drop-off with the S6 isn't as significant from the S5 compared to the Flex2 from the original. The M9 could be WORSE...