This all really depends on your usage and apps.
Coming from a Note8, this sort of spec bump in battery could really mean a full on 24hours without charging, but we'll see.
The Snapdragon845 is good but not great at efficiency and the same goes for the Exynos9810, both are incredibly powerful chips, but are average at power efficiency from what I have seen, this is going by the S8+ vs. S9+ battery tests I have seen, as both have 3500mAh batteries.
How much you use that BT SPen will also be a factor.
I say lets wait and see the GSMArena, PhoneArena and AnandTech Battery tests, all 3 of those together can give you a great idea of where the Note9 stands.
We can use the Galaxy S9+ as reference for now, it did a good job, not the best, but a good job with its 3500mAh battery, so the extra 500mAh in the Note9 should push it quite a bit further.
One thing is for certain, it will beat the Note8.