If it really does have such powerful hardware, the phone is going to need an adequately powerful battery to keep all of that running as well, and Samsung will either have to upgrade the battery itself or look for alternative solutions that can help users get a better experience.
One of the rumors about the device claims that it will come with a special fast charging option to alleviate the problems caused by the faster processor and more memory, but this sounds more like a band aid than an actual solution.
Because, even if the phone does charge faster, this won’t do much to help users who keep getting their battery drained. This will also depend on how frequently/heavily one uses their device, of course, but that powerful processor running in the background will definitely have a noticeable impact on the phone’s performance, even when it’s just idle. In the end, these are all rumors and the phone may not even come with an octa-core processor – we’ll have to wait for the official announcement to find out.