Hot batteries are from wasted energy lost during charge/discharge cycles. Only a very small amount of energy is lost this way. When a battery is full, and sitting idle, it’s cold. Electrical wires are generally cold, they only get hot when huge amounts of energy pass through them and even then the heat is from an incredibly small amount of waste.

This can als me condensed down into - If energy exists in a usable manner inside something, it’s generally not as heat.