I am currently looking at the Surface Pro 6. Before I purchase, I want to know how much it will cost to replace a battery in an $1800 unit. I think the answer to the question may keep me from going down that road.
I have not seen any info on this. My SP 5th Generation (2017) box stated the battery was replaceable. That statement was on boxes for all previous SP boxes.
Microsoft has never, ever replaced just a battery. They have only exchanged for a complete refurb device. While the device is "current" they've been charging around $450 for this. And for the older devices (most likely to have battery needs) I've seen $600 and then they get marked discontinued and there is no way at all to do anything. (Like the SP3, which went from $450 to $600 last spring . I wrote https://digitalmediaphile.com/index.php/2018/04/09/pricing-for-out-of-warranty-surface-exchanges/ in April. If you check https://support.microsoft.com/en-us/help/4023527/surface-how-to-get-service-for-surface and compare the prices to my blog post, you can see how some items are now completely unavailable.
(I'd be curious if the SP6 boxes still show the statement about replacing batteries).
SP3 owners, inflicted with batterygate, tried to get the $200 battery replacements https://www.reddit.com/r/IAmA/comments/26m9cu/we_are_panos_panay_and_the_surface_team_at/chsei5u/
TL;DR see today's Computer World post https://www.computerworld.com/article/3316937/microsoft-windows/it-s-time-for-microsoft-to-fix-the-surface-pro-4-mess-by-offering-no-hassle-refurb-sp5s.html