Why is a remainder shown as an amount and not as kWh?

A remaining balance is held as a monetary amount, not as kWh, because a kWh price can change between two stays. This means 4.80 euros will always be 4.80 euros, whereas 12 kWh at a different price would suddenly be worth more or less. This prevents guests from unintentionally gaining or losing out due to price changes, and makes refunding, carrying forward, and splitting the balance across multiple objects or tariffs simpler. With a single property at a fixed price you barely notice this difference in practice.