48 Hour Rechargeable Night Light

A Laptop Li Cell, TP4056 charge board, and some LEDs walk into a bar

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Premise: use a 3.7v Li-Ion cell from a laptop battery, a TP4056 charge board, LEDs, and either solar or USB power to make a night light that will run for 48 hours without needing a charge.

Sometimes we lose power, or go camping, or just sleep in the camper in the yard wehre there is no power but it would be nice to have a nightlight that doesn't use up batteries. Existing flashlights and lanterns are always too bright.

This design is using reclaimed Li-Ion cells from laptops or other equipment and LEDs to make something that can be on standby until needed and has enough runtime to take partially off-grid or car-charge. The cheap TP4506 charger boards keep us safe - it would be nice to use all recycled electronics but these are just too cheap and good to not use.

Night Light Housing Clamshell v01 20230629.stl

Mirrored clamshell that fits an ~80x80x5mm Li-Ion cell with space for other stuff. Print two.

Standard Tesselated Geometry - 37.39 kB - 07/14/2023 at 01:55


  • 1 × Li-Ion cell of your choice
  • 1 × LED + limiting resistor season to taste
  • 1 × TP4056 charger board
  • 1 × Switch [ optiona| | optionally fancy ]
  • 1 × Housing

  • Magical Runtime

    theonetruestickman07/15/2023 at 18:11 1 comment

    A couple days into our trip I had free time and finished assembling everything into the case and started runtime test.

    • Form factor is a little weird due to the cell shape & size.
    • Brightness is plenty to see by in the dark - brighter than I'd like actually, I ended up putting it under the table pointed at the wall.
    • Not quite as bright as a flashlight though

    After 72 hours of continuous run I went back to check my math. It turns out I mis-read/mis-remembered the cell capacity and it's 13.3Wh, not 3.7Wh, which means I should have about nine days of runtime with the current ~17mA configuration. I guess it meets original design requirements. 

    Future thoughts:

    • Multiple brightness modes could be useful, at least for nightlight/working light levels
    • It needs better physical design for light modes
      • Nightlight - anti-glare/down-light
      • Table/general - diffusion, also anti-glare
      • Flashlight - no diffusion, able to pick up and hold directionally

    I'm not sure if all of those can be done well at the same time or not but it's percolating.

  • Initial Build

    theonetruestickman07/14/2023 at 01:51 0 comments

    Parts were collected, and bodged together. I did this all the week before going camping for a week - I figured that would be a good test.

    Initial math told me with a 3.7Wh cell I should get 48hr runtime if I use less than 20mA, so I used a 220ohm resistor. This gives ~17ma at 3.7V nominal for the cell.

    I whipped up a quick 3d printed clamshell prototype, charged it up, and went on vacation.

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