[Crowbob]

There should be no problem if the CTEK charger is what they call a 'smart charger'. 'Smart' means the voltage output of the charger adjusts itself to the charge state of the battery. If the battery is very low, the smart charger pumps more volts until the battery reaches about 80% capacity (around 12.6 or so volts). Once the battery is at 80% capacity the charger output drops and becomes a maintainer vs. a charger. When the battery is full, a smart charger will also up the volts every once in a while to 'burn off' the plates. At no time will a 'smart' charger over charge (i.e., cook) a battery reducing its lifespan in terms of charge cycles and its ability to hold voltage. In addition, there are usually some very low phantom voltage draws such as the clock or the radio memory that will drain a battery in long-term storage and slow the recharge rate when the battery is connected to the car while charging.

Short answer: if it is a smart charger you're good to go leaving it plugged in and the battery connected to the car. Any time a battery is drawn down to below about 50% (approx. 12.2 volts), the life span of the battery is significantly reduced. The sweet spot is to keep a battery charged between 80 and 100% capacity; not over- or under-charged.