If you're just replacing a battery there's really nothing to do bar buy another one and fit it. Unless you're going off grid and need to produce mains power from the battery you can just forget the inverter. Using them is a sure way to cane a battery as is leaving it uncharged in winter, especially when it freezes. If you can, the best way to care for a battery in the cold months is to remove it from the van and put it on a smart charger in the garage. This will detect and keep the battery in optimum condition, only charging when necessary.