I prefer to remove the battery as you have more control over the temperature its in, ensure nothing drains it, and that it’s always charged properly. BUt, I know plenty of people that leave it in over the winter.
If you do plan to take it out, you’ll want to hook it up to a battery tender to keep it charged. Here’s my step-by-step process for storing an RV battery over winter: https://camperfaqs.com/how-to-store-an-rv-battery-for-winter. I’m also operating on the assumption that you have a lead-acid battery. That article I linked to touches on what to do if you have a different type of battery, ie, lithium batteries.