The 3 amp charge is not doing much to charge the battery in that small amount of time, if your alternator is in reasonable shape. A trickle charge overnight is the best thing to do to your battery, I do my 240D & wife's Jetta overnight once or twice a month. It will not hurt your anternator, jumping a battery with another car or heaver duy charger can cause damage sometimes. But it's rare.
Well it's time to go plug the wife's Jetta into the charger.
