Unfortunately, not all electric mains provides a constant 230V voltage. Even minor variations from the mains can cause the battery to be undercharged or to ‘gas’ (or boil). With undercharging, the negative plate is not fully converted, so some of the material will be inactive. With overcharging, the battery boils, causing it to dry out and the heat destroys the lead plates.
CTEK's primary switch mode battery charger is not affected by variations in the mains voltage, so it will always charge the battery effectively and efficiently.