Four days is stretching what I'd feel comfortable leaving the rats for. I've had to leave them on their own for weekends before when I made trips, but for anything over 3 days I've always tried to arrange a rat-sitter. For one, four days of no attention can make them get awfully bored and potentially destructive.
But if you have to do it, here's a few tips:
1.) Be SURE that your climate control in your house (A/C or heater, whatever season it is) works immaculately.
2.) Have a backup water bottle (or two) just in case one malfunctions
3.) Feed them more than you normally would, and in multiple locations in the cage, just in case something happens to one stash (like the aforementioned water bottle malfunction) they can eat from a different one.
4.) Make up a few challenging rat toys for them to play with while you're gone as they will get bored. I make a few "pinatas" by stuffing toilet paper rolls with treats and tissue or newspaper, wrapping it in newspaper, and hanging it from the cage. It'll at least amuse them for a few hours, if nothing else.
But I really do suggest getting a sitter if you can at all. Sometimes things happen (like your power going out while you're gone!) that are beyond your control and it's nice to have somebody check in, if only for a couple minutes a night to be sure everybody's alive and has food.