You can eat a 4 day old baked potato as long as it has been kept refrigerated during those 4 days.
When a baked potato is not stored properly or kept refrigerated they can develop and harbor harmful bacteria such as Clostridium botulinum which can result in botulism.
As long you refrigerate the baked potato within a few hours of baking them and you reheat them to an internal temperature of at least 165 F before eating the baked potato can be safe to eat.
If the baked potato has been left out for 4 days or even overnight it's considered safe to eat and should be thrown out.
You can also freeze baked potatoes to make them last longer.
When freezing baked potatoes you should allow the baked potatoes to cool and even cut them into wedges or even scoop out the filling of the baked potatoes before freezing to help with reheating of the frozen baked potatoes.
To freeze the baked potatoes, first allow your baked potatoes or baked potato to cool down completely after you bake them.
Allowing the baked potato to cool down completely, helps to prevent excess moisture from forming in the freezer.
Then you can either freeze the baked potato whole or cut them into wedges or scoop the filling out of the potato and freeze it separately which can improve the texture of the baked potato after you thaw it.
Wrap the baked potatoes or baked potato in some plastic wrap and place the wrapped baked potato in a freezer bag or container.
And be sure to remove as much air as possible from the freezer bag to prevent freezer burn.
Once frozen the baked potatoes can be stored frozen for several months.
To reheat the frozen baked potatoes you should thaw them out first in the refrigerator overnight before reheating.
Once the frozen baked potatoes are thawed you can reheat the frozen and thawed baked potato in the oven, air fryer, microwave or even toaster oven.