I though about this project just as I was getting ready for a camping trip. I reached out for the petromax and realised the net was rotten after a long time put away in the shed. Then I looked at the electronics cabinet and found some LED strip and LiPo batteries and immediately decided it was about time I stopped burning fossil fuel for something as simple as lighting.

The final setup is basically two plastic food jars of different sizes, one inside the other, LED strip tucked between them and some wiring to the inside of the inner jar where the battery is stored. The screwcap neatly closes the container making it water-proof (fingers crossed)

Step 1: Getting the Stuff

What you need:

2x plastic screw cap food jars (different sizes) 1£
1 LED strip (I've used 5630 type) ~4£
LiPo battery (3S - 12V) - 10£
Wire
XT60 connectors (or other type if you use a different battery)
On/Off switch
Aluminium foil
Double sided tape

The most expensive thing is the battery which in my case it was free because I already use it for other stuff.

Step 2: Prototype Testing

I've first rolled some strip around the inner container to have an idea of how many LEDs I could squeeze in there - 170 in total. Quick test connecting the LED strip to the battery to make sure everything works OK.

Also confirmed the batteries I'll be using actually fit in the inner container - success.

Step 3: Drilling the Jars

First you need to drill the jars to insert the switch. I've used a super advanced method of rotating a blade to drill the hole in the bottom of the jar, but you can use a simpler method :)

Just make sure that the holes are neatly aligned and you have an even spacing between the inner and outer jars.

Step 4: Preparing the Inner Jar

I have rolled some aluminium foil around the outside of the inner jar in an attempt to deflect some heat away from the battery and slowly rolled the strip around leaving as little spacing as possible to maximize the LED count.

Step 5: Wiring the Setup

Time to grab the soldering iron and the glue gun.

After soldering the wires I have put some glue to insulate everything and keep the power cable solidly attached to the housing.

In the end of the power cable I have installed an XT60 connector as my battery harness, finishing with a bit of shrink wrap to keep it neat and clean. I can later make some adapters to connect to other 12V power sources (car, PSU, etc).

Another quick test to see everything works before proceeding.

Step 6: Closing the Housing

Now you need to close the housing to keep the inner container from wiggling around.

I've used some clothing clips to secure the jars while I applied some glue with the gun. After the glue was solid, removed the clips and added a bit more.

Before finishing the job, I've added a strip of velcro to keep the battery from wiggling around.

Step 7: Handle (optional)

To make it easy to carry the lantern around I've added a handle by rolling transparent tape around and tied a bit of wire to it.

Step 8: Testing

My main worry was keeping the battery cells from overheating, so I've left lantern turned on for some time and then checked the temperature on the inside. Of course one cannot keep the strips from heating a bit but the interior didn't seem to reach unhealthy levels of heat.

At 11.5V the lantern is drawing 0.54 amps out of the battery, so around 6W. I haven't analysed the lumen output, but I would say it's a lot brighter than the 15W CFL I have installed in my workshop.

If my calculations are correct the 5500 mah battery should give me 11h worth of bright light!

Only thing left to test is the water tightness. Of course this is not designed to be submerged. The weakest link in the setup is the on/off switch. I could've used a water-proof switch, but I didn't have any at hand and the idea here was to keep things as simple as possible but would certainly be a good nice to have in case I forget the lantern outside in the rain.

Step 9: LiPo Battery Safety

If you go ahead and decide to use a LiPo you probably already know this stuff, but if not, here are my recommendations.

LiPo batteries require special precautions when it comes to handling and temperature. It's crucial that you follow all the safety recommendations of the manufacturer.

Pay special attention to the following aspects:

Never let the battery discharge completely - most electronic equipments feature minimum voltage cut-off circuitry - this setup doesn't have that. When the light starts to fade, turn it off (better yet, don't even let it reach this point).
Be specially cautious in keeping the battery protected from sharp edges
Never leave the battery unattended - LiPo batteries are known to explode/ignite especially if misused. As a precaution keep an eye on the battery at all times.