Lori from North Gower, Ontario has purchased an old farm house with one part covered in board and batten wood while the main house is brick. She wants to know what she should do to protect the old board and batten. Presently it has simply been left to "silver" with age.
Painting or oiling that old siding could help to slow down the cracking that happens (technically called "checking"), which could reduce a bit the water that will penetrate to the back side. But if you look carefully at any siding like this that has been around for a long time, it is not the visible surface that eventually rots. It is the part of the board that sits in the snow, or the backside where it is holding tightly up against another board, probably the strapping behind.
In the photo I show an old piece that is still rotten where the attachment was despite having been painted. Painting or oiling on the outside has little effect on this weak point, unless you do it before the boards are put up -- and even then this is still the weak point. Most modern board and batten siding is pressure treated to eliminate the rot question.
The real key to these old houses working is keeping them dry. That old barn siding has lasted so very long because it dries so quickly between rains. Keep snow drifts off of the wall, that is in fact why in the photo you can see that the boards stop so high up from the ground. If you want to coat it, remember that you are mostly doing it for looks, and you will have to keep up that finish every couple of years.