How do you charge a battery on a softail?

Your best bet is to take it to a competent center that has the ability to charge the battery for you. Most auto parts stores can do this. Tell them you want a slow charge, as this is the best and safest charge for the battery. Lastly, invest in a good trickle charger... Battery Tender is the best on the market, and can be had for about $25-$35. It wires into the battery by two simple wires (positive lead to the positive battery terminal, negative lead to a good chassis ground). Then, all you have to do is plug the Tender into the pigtail you just installed, and then into an electrical outlet. The light will be red when charging, solid green when fully charged. There is no need to monitor it, as there is an overload protector that prevents the battery from getting overcharged. You just unplug it when you get ready to ride, and the battery is always fully charged. Furthermore, this prolongs the battery life considerably, which will save you money. Ride safe!