In the past few years there have been quite a number of Lithium Ion Battery recalls, and a disturbing number of laptop computers have basically exploded because of catastrophic battery failure. There aren't many things scarier for a pilot than an in-flight fire. You can't just open the doors and get out at 30,000 feet, and you can't open windows to get breathable air, either, on an airliner at altitude. Even for small planes, which fly at lower altitudes, aren't pressurized, and can land pretty quickly, the prospect of an in-flight fire is terrifying. There is no place to escape to. I do have several hundred hours of pilot-in-command flight time, and an in-flight fire is something you train for and then pray it never happens. Lithium cells are wonderful in terms of how much energy they can store for a given volume and weight. Unfortunately, the more energy you have stored in a given space, the more havoc happens if it is catastrophically released, either by an accidental external-to-the-cell short circuit, or an internal failure in the cell.