If you have a currency backed by some good, you need to be able to exchange the currency for the good. How would it work? There's no consistent price of energy

If you have a currency backed by some good, you need to be able to exchange the currency for the good. How would it work? There's no consistent price of energy, as it depends on the cost to get it to you and the local method of generation. I suppose you could give them batteries, but now you're back to tying it to a physical good, one which has some irritating problems like toxicity and losing the charge over time. You're probably better off choosing some arbitrary material that's in demand, which is how gold and silver got into use.