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I've got a cheap LED lamp running on three AAA NiMH batteries which stops working when exposed to near-freezing temperatures; is there a likely reason for this?

LED lamp assembled Internal circuitry

The lamp has been dropped a number of times due to my incorrigible clumsiness and the batteries are a year or two old; could either of these factors play a role?

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    Batteries don't like cold, especially when they're aging. And cold changes the resistance of electrical components. Normally the resistance goes down, which one would think is good, but the change in resistance of one component compared to another could upset the balance of the circuit. – Daniel R Hicks Nov 30 '16 at 21:58
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    NiMh are nominally 1.2V, which will decrease with temperature. Alkalines are 1.5V. A cheap torch such is this will be designed to run of the higher voltage (1.5V) cells. Switching to non-rechargeable Alkalines would almost certainly fix the problem. – mattnz Dec 1 '16 at 0:44
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    @errantlinguist yes - but if the light starts the cold ride with its internal temperature at room temp, rather than being left on the bike overnight and starting the ride at cold-garage/shed temp then it might run a bit better, at least until it cools down. – Criggie Dec 1 '16 at 6:53
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    Does it dim slowly or does it go out suddenly? If it dims before going out I'd suggest the battery, but if it's sudden the issue could be thermal contraction of the metal either breaking or shorting a circuit. – Jamie A Dec 1 '16 at 17:47
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    @errantlinguist Instead of spending money on diagnosing why your cheap light doesn't work, just get a decent light. – David Richerby Dec 2 '16 at 9:48
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There are two reasons why it might not work:

  1. The batteries don't like the cold. Many battery chemistries don't like the cold -- notably alkaline, manganese (heavy-duty), and NiMH/NiCad batteries. To test this hypothesis, put your light (or even just the batteries) in your freezer. If your light gets weaker the colder it gets, this is your problem (especially with cheap lights that don't have step-up converters). You can pre-warm your batteries or switch to a chemistry that is more cold-resistant - such as Lithium. Lithium is stronger in cold weather, but not invincible so again you may want to pre-warm your batteries. Unfortunately, lithium AAA 1.5v replacements are quite expensive and not rechargeable. You might be best getting a new 18650 lithium battery rechargeable light.

  2. If the lights turn off in the cold even with fresh batteries, then you may have a faulty solder joint. As the light gets colder, the components in it shrink at different rates and it's easy for an electrical connection to break due to bad soldering. This might only happen when the light is below a certain temperature. If the light flickers or turns off at a certain temperature (rather than dimming), then you most probably have a poor connection. While you could resolder or reflow the solder, it may be just easier to get another light.

tldr; You need a new light. Get a new one based on 18650 or larger, rechargeable lithium batteries. As David Richerby notes, buy the best light you can afford. You'll save more over the long term as money buys durability.

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  • A cheap light designed for 3 AAs (3.6--4.5V fully charged/new) will usually run very happily off a 14500 lithium cell (with spacers) . That's how my helmet light runs as I built a rear light into the battery box and dropped to a single cell to make space. – Chris H Dec 3 '16 at 14:29
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    I changed out the batteries and it still doesn't work, so it must be no. 2. – errantlinguist Dec 5 '16 at 9:29
  • "You need a new light", preferably a dynamo driven one. I've never had problems with my lights due to temperature or empty batteries... I wouldn't say that dynamo driven lights are robust as the typical wires that you get for bikes are just plain shit. But with a battery powered light, you must remember to charge it ahead of time, and you must not forget to take it with you. With dynamo powered lights, you just switch them on when you need them. – cmaster - reinstate monica Jan 2 '19 at 10:06
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Batteries, especially most types of rechargeables don't work well in cold conditions. The chemical reaction that powers the electric voltage does needs some temperature to perform as intended. If you then have a consumer load that requires a bigger amount of power, they tend to drain rather quickly since they cannot set free much energy when cold.

You could try with newer batteries, maybe yours are already a bit exhausted or you can try ones that are based on a different cell type.

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    You can try lithium based cells which are much more expensive but also more cold resistant. – Carel Dec 1 '16 at 20:35
  • Lithium batteries perform quite well in cold weather, as Carel pointed out. I've got rechargeable lithium batteries on my bike and an outdoor weather station that perform just fine in sub-zero (F) weather that would kill most other types of batteries. – Carey Gregory Dec 4 '16 at 15:37
  • Excellent advice, but it seems that the light itself has given up the ghost; see RoboKaren's answer. – errantlinguist Dec 5 '16 at 9:30
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    Sub-zero (F) is definitely sub-zero (C) and thus is redundant, although you might be differentiating from sub-zero (K) and aiming for a Nobel Prize. :-) – RoboKaren Dec 5 '16 at 23:57
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I have had this problem with cheap LED lights while biking in cold weather. They seem to only fail when in "blinking" mode, so my solution has been to keep the lights full on.

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