Will skim milk powder go bad when mixed with peanut butter? I love to make those peanut butter energy balls to take with me on camping trips, or even a day fishing or after a long run. If I add skim milk powder to them is there anything that will make the skim milk powder spoil? I never refrigerate these and won't be able to.

By the way, these are really cheap to make, taste amazing and offer loads of energy and protein while being healthier than candy bars

I have my own recipe but the standard recipe appears as a Google result when searching: peanut butter energy balls

It is basically: oats, peanut butter, chocolate chips, and then whatever you want. No need to bake them.

I would think since there is no water, the skim milk powder won't go bad. I always thought it would be great to add a little bit of it for extra protein to help keep me feeling full on long camping trips without buying a lot of expensive products like beef jerky or protein bars.

I couldn't find this question asked via Google so I joined here to ask :)
I would think that you'd be okay adding non-fat powdered milk to your energy balls. Powdered milk, when mixed with other ingredients, will last as long as the quickest expiring ingredient it is mixed with. http://www.eatbydate.com/dairy/milk/how-long-does-powdered-milk-last-shelf-life/
It doesn't sound as if there is enough liquid in your energy balls to reconstitute the milk. If you are really worried about it you might consider adding a whey protein powder to your energy balls instead of the powdered milk. Although those tend to be more expensive.