I too have similar problem from day 1 of the purchase; I reported immediately to the seller and Microsoft too. Today is 17th day. I tried whatever said above with the help of the tele-executive of Microsoft Call Centre, but to no avail.
Rate of discharge is almost 1% per minute of usage. Despite trying hard on available options, I'm yet to find a solution.
Microsoft Call Centre finally offered for a replacement with refurbished Surface Pro 8; wonder why I paid for a fresh one while I'm getting a refurbished for a fault of Microsoft own product.
On contrast, I've been using MacBook Air for last 6 years; not even a single complaint on the hardware - not exaggerating.
Please let me know if there is a way out to improve the battery life without going for the refurbished one. I hate to go for it.