Each Nanolantern uses three LR44 coin batteries.  One set of batteries will last up to 60 hours.

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To replace the batteries: 

- Unscrew the crystal counter clockwise from the base (this is how you access the stash spot)

- Slide out the LED & Battery component from the enclosure.  A slap on the palm usually does the trick.  But if its a little tight, don't bust out the lube quite yet, grab some tweezers or needle nose pliers and grab anywhere EXCEPT the LED itself.  There is a shroud around the base of the LED which is a good place to pull.  

- Pop out the batteries and replace.  

- Slide the LED and Battery component back in, lining up the button on the device with the button on the case.  Again, no lube necessary.