Car battery failure

Hmmm, yes, you know those motorcar batteries with the 12 month warranty. Well mine just died at 12+1, AGAIN. Now another 500 or 600 is to be wasted on having to a replacement. The battery centre manager is quite confident that my car electronics is at fault because he feels a constant 100 - 200 mA is too much to maintain all the complex electronics in the car when it isn;t running. As with most similarly sized batteries it should be able to do 60 - 70 Amp hours which gives it at 150 to 200 mA almost 2 weeks before it should run itself down. Thus it is not possible to damage the battery if it only stands for 12 hours max at a time. And of course I travel at least about 20 to 40 km per day so a complete charge is always possible (yes, the alternator checked out). Shall we argue that the winter weather did it, maybe, if you consider 15 to 20 degrees C a cold winter. In fact, that is a very healthy temperature for a battery to maintain. So I wonder how these people come to their conclusions. A page from http://www.solar-electric.com shed some useful info on lead acid batteries, although it isn't very detailed, it is quite clear that something other than my car is at fault...