Primary Cells

Primary cells are 'single use'. They are not rechargeable. An example of a common primary cell would be a AA Eveready Lithium Energizer, or a AA Duracell, etc.

GP Brand, CR123A: $3.50 (14g)
Placed in series, these 3v batteries are also commonly used to replace one 18650 cell in devices that can handle up to 6v, such as the Spark Headlamps.

Best use scenario...

Primary cells, used all the time, can become expensive. However as they are light weight, safe, store well, and last longer than the equivalent rechargeable, they are a good backup to carry in your pack, just in case you need them in an unexpected event.