The LOAD or light in this case, regulates the power. A good load incorporates a good regulator or power converter for safe operation. A cheap load produces grief.
I like the 18650 cell. Long life and rechargeable. The high current capability of the 18650 must be respected though. Throw a fully charged cell into your pocket with keys and you'll have something like this ..,
A safe way to carry spare 18650s is found at walmart in the camping section
A re-purposed waterproof match case with a 18650 fit.
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