If the website may be used in mobile, tooltips may not be a good solution since most are initiated by some kind of hover.
If the information can be conveyed after the button is clicked, perhaps a toast notification could help. This provides an immediate notification upon interaction which will likely satisfy the user, but be passive enough to ignore if so decided.
If not, maybe a label with a dotted underline could be used to indicate to the user that there is a touch opportunity to explain further the function of the button. Clicking the label could pop up a tooltip to explain the consequences of pressing the button, without having to make the choice of clicking the button.
If the button is in only a single (or few) spot(s) in your application/website, perhaps just a brief description next to the button would provide the best user experience. With this option there is no barrier to provide the user with all the relevant information about the actions of the button.