How long the SP7 battery lasts is a difficult question to answer because no one reports their settings in a detailed manner (level of screen brightness, power mode used, wifi on or off, bluetooth on or off, keyboard attached or not, dark mode on or off, number of background apps open or closed, type of software installed, etc.) or systematically outlines their usage. As an owner of a SP7 (i7, 16ram, 256ssd), 2020 SPX (SQ2, 16ram, 512ssd), and 2021 SG3 (Pentium Gold 6500Y, 8ram, 128ssd), I can tell you that the SP7's battery life does not compare to the latter two devices. I easily get 13-14 hours of continuous YouTube viewing (40% screen brightness, battery save and wifi on, Bluetooth off, no keyboard, all background apps closed, dark mode on) on my SPX and over 9 hours on my SG3. With my SP7, battery life has ranged from 5 to 8.5 hours and currently stands at 6.5 to 7 hours.
In trying to manage my SP7s battery life, the main problem appears to be Windows updates. Some updates have a very negative effect on battery life. Consequently, I am constantly installing and uninstalling updates to figure out which ones are impacting battery life. Sometimes uninstalling updates helps, sometimes it doesn't, and other times it makes things worse. I ended up purchasing Anker's PowerCore III Elite 25600 87W Portable Charger as a way of extending my SP7s battery life. The Anker portable charger confirmed that the SP7 is a battery hog. The SP7 drains the 25600 mAh battery in a little over 7 hours, whereas my SPX, SG2, and 2020 HP Spectre x360 laptop all take between 10-14 hours.