Camping and Backpacking GEAR thread

Improved Glow Stick
A cheap, reusable 120 hour glow stick

Been meaning to share this. Sometimes I want to mark a cairn or cache that I'll need to find later in the dark.

A classic option for this is a chemical luminescent glow stick. These are reliable, weather proof and last about 12 hours though you if look hard enough you can find different chemistries that burn slower and dimmer or brighter and shorter. They aren't reusable of course though. And if not packed correctly can activate before you need them.

Recently a number of manufacturers have made LED versions of these powered by button cells. They also typically last about 12 hours but then you can replace the batteries and use them again. Some of these offer fancy blinking options, multiple modes including a flashlight and some of them also have a automatic timer that turns them off. That last feature is annoying if you can't disable it!

Some of the fancier ones include a current mode driver for the LED which ensures even illumination over the life of the batteries as well as making the batteries last longer. The cheapest ones directly connect the LED to batteries and so start out extremely bright when the batteries are fresh and thus drain the battery much faster than necessary until they start to become rather dim.

All of these options as offered suck for multi-day use such as placing a cache three or four days before reaching it or wanting to mark a return point on a multi-day trip. Or if you are using them as a nightlight or toy for a kid on a trip you will burn through a bunch of batteries fast.

I'm a EE so the suckiness of these choices annoyed me to no end. I thought about modifying one to be more efficient or only turn on in the dark or whatever. Fortunately I found a much easier and more elegant solution...

Step One - Start with the cheapest stick possible

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The first thing to do is start with the cheapest, simplest sticks that do nothing other than connect the LED to the batteries. The above made by Life Gear are what you want. They make many versions, including fancier ones that blink and do all sorts of other stuff. Give those a pass. Get these ones that you screw to turn on. Available in red, green and blue. They are available at places like REI but also this time of year (Halloween) they tend to show up lots of places for cheap (like $3 a pair). I got mine from Target a number of years back for $1 each.

Now the beauty of these is they will not try to outsmart you by turning themselves off after some amount of time. They just smoosh two contacts together when you screw the top down so the stack of three button cells are connected directly across the LEDs.

The problem as mentioned before is that this direct connection draws way too much current when the batteries are fresh (about 90 mA in my measurements when 5 mA is more than enough). If only there was an easy way to fix that.

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Step Two - Get the right batteries

It turns out there is just the right kind of battery to solve our problem with too much current and at the very same time also one that stores way more energy than the typical button cells. Unless you have hearing problems you probably don't know about them.

The Magical Zinc-Air Battery

Zinc-Air batteries have three times the energy density by volume than any other battery chemistry. That means for the little button cells these lights run on they can run for at least three times longer (but actually it is even better than that, see below). Why then doesn't the whole world run on Zinc-Air batteries? Well there are a few issues with them. The first is right in the name - "air" - they need oxygen to work. They are actually more like a fuel cell than a battery and they "breath" the air around them to work. A related problem is that once exposed to air they start working whether you need them or not. They come with a seal on them and once you remove the seal you better use up the battery in the next few weeks or it will be dead. This is just fine for a camping light though - tear off the seal at the start of your trip and throw the battery away at the end.

So what are they used for? Well, they are primarily used in an application that has nearly continuous use and where a really small power source is a plus - hearing aids. You'll often see them referred to as "hearing aid batteries" and will most often find them in the pharmacy section rather than with the rest of the batteries. Another reason they are probably overlooked.

One heck of a bonus feature

Remember how the I said above the simplest LED sticks drain way too much current with new batteries? Basically there is no current limiter in the circuit so the LED sees the full voltage of the fresh battery and uses the internal resistance of the battery to current limit. With fresh batteries this isn't enough limiting and they run really bright and rapidly drain the battery. After an hour or so the battery has had nearly half its capacity drained but now the voltage lowers and so the LED draws less current and this is how things run for the remaining 10 hours or so. Some fancier LED sticks have circuitry inside them to try to better manage the current and so these can make things last longer but a number of these same sticks do annoying things like turn themselves off after an hour! Not what we want!

Well the Zinc-Air has one other awesome "feature". It is more like a fuel cell than a battery so it's output current isn't limited by an internal resistance like a typical battery. Its current is limited by how quickly air can get inside battery cell to react with the electrolyte. Basically the current is limited by how many and how big the holes in the case are. It turns out since these are designed for hearing aids this limit is almost the perfect amount to illuminate the LED. Better still this kind of current limiting does not waste any energy like a resistor or linear current regulator would - so it is extremely efficient.

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Putting it all together

These Zinc-Air batteries for hearing aids are pretty cheap. About $0.33 per battery in quantity. A glow stick takes three, so that's just $1 per use.

The glow stick itself costs between $1 and $2.50 depending on when and who you purchase it from. You'll reuse it multiple times of course making its long term cost essentially zero but they are still so cheap that if you lose or break one it is no big deal.

And how long does it last? I've tested them multiple times and their run time is more than 120 hours!!!!

They actually run a lot longer than that but of course they eventually start to dim. After five solid days of continuous use they are still just about as bright as they are when first used. Do be aware though when you first turn one on it will be unusually bright for a few minutes because there is plenty of ready power in the fuel cell from oxygen stored in the cell. It will take a few minutes to deplete that and have the current limited by oxygen entering the holes in the battery case.

Again once you remove the pull tab seal the battery needs to be used within a few weeks. In my tests I've run them continuously for five days without turning them off to evaluate their total energy storage. In the field if I'm using them as a night light for my daughter or to mark a campsite at night I typically turn them off during the day. I've run them after such a trip and verified they can at least hold their charge for up to two weeks from removing the seal.

Last careful where you purchase these batteries. They have a more limited shelf life than most batteries and a lot of online vendors like to sell near expiration batteries at a discount. This is fine for a hearing aid user because they naturally use a lot of these fairly quickly and so buying a near expiration battery is no big deal. For an infrequent user like me that's not what I want so I make sure to buy from a reputable online seller or just go to the pharmacy where I can see what the expiration date on the package is.

 

I've got boxes of these batteries on their little cards here left over from my fathers hearing aids. now I have a reason to keep some to play with. Thanks mate, yer' a legend because I now have an inexpensive project my my sons scout den.

 

This is awesome! Since you seem to be the man in the know on these batteries, could you reseal them to stop the battery drain. I guess choking out the needed air and then removing the seal later and the air restarts the battery? If necessary, forgive my ignorance.

 

Great question! I've not tested this but the answer seems to be mostly yes but how well it actually works and for how long is kind of unknown.

On hearing aid websites this appears to be a common question and many users do in fact report that if they don't use their hearing aids continuously they get longer life by taking the batteries out and covering them with tape. In these cases they aren't really resealing them for a long period though so I don't know if it really is effectively stopping the reaction entirely or just slowing it down. Some folks use the original tabs that came with the batteries, others use scotch tape and some even just use putty or wax.

This document from Duracell does specifically state that resealing can extend the life of the battery when in use:

So I don't know if you say used 40 hours on one trip and then resealed the battery for a few months whether you'd get another 80 hours out, or just 40 hours or none at all.

 

PanAmerican travel group I’m a member of had it. Agreed on the laundry list of questions.

 

Something fishy if they have to pay to get someone for an adventure like that.

 

I imagine they’ve already sold it to a large network and have been fronted a large-ish budget. Honestly, if I wasn’t out of their age limit and on dialysis I’d have inquired and been happy with expenses paid.

 

And with REI charging so much for a weekend backpacking trip..... I do not think they have a shortage of applicants.

 

Agreed, I imagine the applicant list will be long with experienced outdoor types that have fluffy IG and YouTube accounts.

 

And the proper pink goretex.

 

Too old for their requirements but that does sound interesting. Be interesting to see the final product.

 

I'm too old at 44 and to busy with life. The age requirement is kinda funny though. One of my favorite things to do is watch a 20-30 something get shut down on a hard climb. Then they get to watch the old guy float it. Being fit and being old are not mutual exclusive. I've worked hard to stay in shape and keep climbing harder every year. I know I'm doomed to have that go the other way eventually but I'm determined to push it off as long as possible. lol

 

I've got a buddy who's 65 and outhikes anyone I know. Not simple short hikes either. 20 mile Eastern Sierra jaunts aren't a big deal to him. Very inspiring.

 

I would go to be filmed for their reality TV-show

however if my single glass eye fell into the water and was swallowed by a fish, it would ceartinly make for an interesting plot-twist in the story

 

An Arc'teryx eye patch would look really cool with the bird on it.

 

@MTgirl do you by any chance have a close up pic of how your RTT is mounted to your 4runner? Is it mounted to the stock rails?

 

OK so you're using more than just the stock rails. I was concerned there might not be enough room for the tent bolts because of the lack of clearance between the stock rails and the roof. Preeeeesssshh ate it!