When I travel I take two: a single-cell light that goes into my pocket, while the longer two-cell version is clipped onto the outside of my personal carry bag (which also serves as my first aid kit and camera bag; whether home or away, that bag is always with me!) The two-cell is always immediately at hand when the bag is with me, and the only time the single cell isn't on my person is when I'm taking a shower!
...The two-cell versions are longer than an equivalent lithium (123-size) light, making them better defensive tools, and both of them use batteries that are more immediately available wherever I go.
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