Mark it depends on the design of your charger, as to leaving on when charged. The one I use is designed for being left on the battery for long periods and will maintain the battery in a fully charged condition for extended periods.

As for most German cars of the 90's, the cig lighter stays hot when car is turned off. All VW's have been like this for 10 to 15 years. The .05 Amp solar charger that comes with VW's is too light duty to charge the battery much, but will carry the load of the electronic system drain while the car is parked. Someone who had to park a car for an extended period, can't remember exactly how long, but it was somewhere between 6 to 12 months. Anyway the battery, which was fairly new, drained durring this extended period.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.