My wife's car is often not used for a couple of weeks and even though the battery is fairly new, its sometimes not able to start the car because of lack of volts. This situation is not helped by the fact that she only drives short distances.If I remember, I take the car out for a run to charge it up. I've seen solar powered car battery chargers which trickle charge the battery via the cigarette lighter. Does anyone use such a charger ? and what are the best ones - 1 w / 1.5w / 2w or what ?