How long to idle to charge battery?

How long do I need to idle the bike to charge the battery when not riding it for a couple of weeks? I try to ride all year in Colorado but there are some weeks when it is just colder than I want to ride. This morning I wheeled the Canyon Dancer out of the garage door and let it idle for about 10 minutes then shut if off and rolled it back in the garage. Am I using more battery to start it than I am putting back in with the idling? I have a battery tender (Schumacher) but am using it on my classic car right now.