I'm surprised people are having such problems with their batteries; we've had 12 year old cars (and some slightly younger models) and never had any problems with starting. I've never had to buy a car battery in my life (touch wood). If the battery is shot or on the way out I'd just get rid of it, without delay. Unless you have cars which don't get much use or are used intermittently I wouldn't see much point in buying power packs etc. If the car is used regularly and the battery looked after (if this is even necessary now with modern batteries?) you shouldn't have any trouble. Batteries won't just fail overnight. A lot of people don't realise that if they have a lot of electrical equipment on (particularly heaters/ defrosters etc) that their battery is more likely to run down, particularly on short runs during cold weather- the battery just won't achieve full charge. This is especially a problem as cars are now packed with electrical goodies- all of which can be a substantial drain on the battery, more so in cold weather.