...but, the 'new-age' conditioners such as the Optimates, are perfectly OK to leave on over the winter for example. The micro-current they do provide is only provided when the battery needs it, not all the time.
The term 'provide' as used above needs putting in the context of electrical theory. The conditioner, in fact any 'power supply' device, only 'provides' the current that the thing it is connected to wants to 'draw'.
There is a huge misconception among users (of power supplies of all sorts and especially in the world of 'finicky' computerised telescopes) that the supply, or charger, somehow 'pushes' current into the device in question. In fact it merely 'allows' the current to be 'drawn' by the device, in our case a battery. So, a 20 Amp power supply will only provide the correct current for a 1 amp device; it won't somehow blow 20 Amps through it and destroy it.