Template Sensor Cost Increasing When No Energy Is Being Consumed - EV Charging

Hi, I’m looking for a bit of help.
I have a Pod Point wall charger. The integration has a current energy being delivered to the car sensor. I have created a cost today sensor which utilises the Pod Point current energy to calculate the spend for that day. I also have dual tariff electric (night rate between 12:30am and 4:30 am and day rate at all other times). The car usually completes charging around 2:30am. I also have a input_number that holds the correct cost of electric (which gets updated to new values at the correct time of day/night) - this is either 0.075 or 0.40.

While the cable is connected to the car and the car is charging and the rate is night the sensor calculates correct cost. However, when the input_number changes to day rate value (4:30am), even though the car is not receiving energy (as it is full) the cost sensor value recalculates the entire energy added to the car at the new day rate. How do I stop this from happening?

Cost template sensor:

    - name: "EV: Cost (Today)"
      unique_id: bf10678c-e7ae-4a7b-90ad-9180a8e96729
      device_class: monetary
      unit_of_measurement: "GBP"
      state_class: "total_increasing"
      icon: mdi:cash
      state: "{{ (
          states('sensor.ev_daily_energy') | float 
          * states('input_number.octopus_go_now') | float 
        ) | round(2) }}"

Current energy sensor (the break in the line is due to HA upgrades), the drop to 0 was due to unplugging the car:


Cost sensor (the break in the line is due to HA upgrades):