But the good thing about the CTEK (and other good quality conditioners) is that they are well able to top up your battery charge in a few hours, so I tend to plug mine in if I'm planning to use the car the next day and I haven't driven it for a while.
Unless it's below about 9V, I believe. You then need a charger instead of a conditioner to bring it up to the required voltage. At least that is true of the CTEK I have.
