My favorite spare carrier is a 2nd flashlight first followed by an old pill bottle.
good idea ;-)
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A note about spare batteries, CR123 vs 16340.. (simplest to carry the same chemistry as in the light)
If you run the light on LiIon but choose to carry CR123 as a backup
You must take deliberate action to turn off the LVP when you start using CR123 after LiIon..
because
If the light is running on LiIon, the HDS driver enables LVP for LiIon automatically.
(LVP shuts the light off when voltage drops below 3V, but a CR123 is still more than half full at 3V)
If you switch to a CR123 battery after using LiIon, the LVP does not turn off automatically. You must do a battery detect reset when switching to CR123
here are the instructions to do a battery detect reset:
"No special actions are needed to use rechargeable Lithium-ion batteries. Your flashlight detects them automatically.
However, if you have been using rechargeable Lithium-ion batteries and want to return to using regular (non-rechargeable) batteries, you must perform a reset. The simplest way to perform a reset is to turn on your flashlight (with the button released) and open the battery compartment until your flashlight turns off and then replace the battery compartment.
If you fail to perform a reset when returning to using non-rechargeable batteries, your flashlight will act as if the new non- rechargeable battery needs replacing – just do a reset to restore normal operation."