The Battery is all about, you guessed it, batteries. Turns out they have a fascinating history and Schlesinger tells it well.
One interesting police note:
In the late 1800s, Conrad Hubert ... [and] his American Ever-Ready Company teamed up with a David Missell.
Missell and Hubert's innovation was to house their product around what would become known as the D cell battery in a tubular design, making them lighter than square wooden or metal cases of bicylce lights and easier to carry.
Lacking neither ambition nor nerve, the partners promoted their flashlights by giving them away to New York City policemen and then collected testimonials from the patrolmen to use in advertising. The light was an unqualified success. (pp. 181-182)