You are holding a laptop for someone who will be away from the country for around a year. What is the BEST technique to preserve the life of the laptop battery?

Extreme temperatures will reduce battery life, whether they are hot or cold. It is best to store batteries in cool (not frigid) temperatures. You might think that freezing it would be the best option, however, freezers frequently have too much moisture and are too cold. A closet is at room temperature. A battery should be stored someplace dry that is only a few degrees cooler than room temperature. When you store it, it should be about half charged. You should periodically bring it out to charge and discharge it before re-storing it.