Mild hybrid cars

My son inherited one of the first hybrid cars. It must be going on 15 years old .It had an enormous battery, which I believe is expensive to replace, but cross fingers the car still goes very well

A mild hybrid is a petrol or diesel car with a starter/generator plus a larger battery to store power produced engine or by regenerative braking. Many brands use it on the “ECO” models, unlike a full hybrid they cant drive on electric only but give around 10% better fuel consumption.