About tea light LED runtime

My next door neighbor put out a bunch of LED tealights along their walkway on Christmas Day and left them turned on. They were inside little cardboard enclosures. After Christmas, they were left turned on and eventually they got blown around and buried in snow. Now, a whole month later, I found one in my yard, still turned on! A month is 720 hours.

I brought it inside and tested the battery, which is a 3V lithium CR2032 and it actually has plenty of juice left in it.

Then I looked up tea lights on google that use these batteries and the specifications always say they last for 100 hours. So why is this particular one still going after a month? Does cold weather make it last longer?

Is it solar? Maybe it got some light through the snow?

Racer said:

Is it solar? Maybe it got some light through the snow?

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It's not solar. It runs on a CR2032 battery.

My guess is they underrated the runtime a bit, and the excess cold slowed down the chemical reaction inside the batteries enough to lower the voltage a bit (with a large decrease in current draw due to the non-linear nature of an LED's forward current/voltage relationship)

Cold would increase the LED Vf, which in turn would decrease current, perhaps to less than 1/10th what it would be at room temperature.

Interesting. I didn't know that.

Neat!

I power a green LED off of 2 AA batteries as a indicator to be sure I put my garage door down at night. It is attached to the inside of the garage door and I can see it from my front window, through the side window of the garage. I'd have to go outside to enter the garage even though it is attached to the house. Anyway, it will run for nearly a year before it gets too dim to see. I could see the Tea light going for a month on the coin cell.

JohnR66 said:

I power a green LED off of 2 AA batteries as a indicator to be sure I put my garage door down at night. It is attached to the inside of the garage door and I can see it from my front window, through the side window of the garage. I'd have to go outside to enter the garage even though it is attached to the house. Anyway, it will run for nearly a year before it gets too dim to see. I could see the Tea light going for a month on the coin cell.

Click to expand...

That does explain it! Yeah, the temperatures were getting pretty darn cold, around -15 some nights.