Have used one now for more than 10 years, they are a must if you have an alarm system in the car. Last battery lasted 5 years with the car traving under 100km. Have four units in total, including one on the Jet Ski. Before the C Teck or similar could only achieve under two years battery life. It was replaced under warrenty but told not to come back. I swear by them, Have mates who also use them on their show cars.

The CTEK units will NEVER "overcharge". The electronic systems will not allow it.

Hi all, all 12v batteries and all others should have 2v per cell of the battery. Those cells should when fully charged show 2.2volts each cell or they overcharged,undercharged or defective(dead cell, or short circuit). If you overcharge you will melt the lead plates to the point negative touches positive in the cell and the battery is ruined. A lead acid battery should never be under charged as it will soot up with lead deposits and the longer they are left that way the worse they will get. 
Trickle charge is the best way to maintain a battery when not in use, whilst it won't replace general use as a substitute and no battery will ever last forever. The thicker the plates and structure of your cell, determines your battery life and you can only cycle that recharge(charge your Battery) a certain amount of times. 
You can also desulphate a battery at the same time as charging which aggregates the lead cells to release their caked on energy but this must be done while charging or in a charged state.
So to end battery should have 2volts each cell, should be kept at full charge, should never go below 50% charge, should never be overcharged,and trickle charge with desulphation has had me bring industrial batteries back from the dead that are 22years old(These are deep cycle so bigger and better plates=Longer and less maintenance battery)
Also note I spend thousands each year replacing batteries because they do have a life span and cheap=nasty
Keith