Another clue that the Galaxy S6 will feature a 2,600-mAh battery
http://www.androidauthority.com/samsung-galaxy-s6-battery-capacity-588376/
Why would Samsung reduce the battery size of the Galaxy S6? The answer may lie in the phones sealed construction and 6.9-millimeter profile. These design constraints probably forced Samsung to shave off the size, and implicitly the capacity, of the battery inside the S6.
In theory, the 14nm Exynos processor expected to power the Galaxy S6 should consume less power than previous generations, partially offsetting the decreased battery capacity. Then again, the reverse applies for the Quad HD screen, because higher resolutions translate into higher consumption. So well have to evaluate the entire package before we can issue a judgment on the Galaxy S6s battery life. And that will only be possible after March 1, when Samsung will lift the veil of the S6 and S6 Edge at its MWC event.
You have to also consider that they're going to apparently set the standard for wireless charging. So charging will be easier.