I’d appreciate suggestions for a 1xAAA backup light for an Appalachian Trail thru-hike. My preference is for about 100 lumens, waterproof, tail cap switch, spot/flood, three or fewer settings, around $30. Or as close as possible.
Thanks.
What about the Manker E02? Seems to fit most of your requests 
Several come to mind (I’m a fan of the AAA click space), with a bunch just being announced this year
For angle head lights:
Manker E02 - 20
Lumintop HLAAA - 20 (less with coupon)
For regular straight lights:
Lumintop Tool (all time favorite with good reason) - 10 right now
Thrunite Ti5 - 20 if you can find one
Zanflare F3 - 10?
Manker E21 - 30 (1 or 2 AAA)
Those are what come to mind, I would go with the Tool with a Nichia, very nice light for cheap. Buy two at that price if you want a backup to the backup, they’re nice to have around anyway.
If you can afford the weight, I would look into the AA size for the increased capacity, but I know with through hikes every oz is calculated
Thanks folks. I looked at these and it gives me a great group to choose from. I am considering 1 x AA. I have an AA headlamp and an AA camera and I have to decide if I want to use only AA electronics (cheaper), switch to all AAA (lighter), or carry both. I need a headlamp for my wife and may carry a weather radio that uses AAA. Our backup for the backup will be 2 coin-cell Photons we already have.
Thanks again.
If space is not much of an issue, I’d go with an AA light, as it has got about triple the capacity of an AAA light. Of course it’s “just” a backup light, but in case you actually need to use it, I can imagine you will appreciate the additional capacity.
Initially, I want my backup light to have the same power source as my main light. For example, if my main M43 light with 4x18650 cells dies, then I’d like to use my backup light, for example Emisar D4 with 1x18650. I can use the 4x18650 cells all for my D4.
Zanflare F3, buy 2 pcs for 20$ and you have double back-up :sunglasses:
I’m nowhere near a thru-hiker, but I did a very small section this past summer with my wife. We each had a headlamp (Boruit RJ02) and as a backup light we each had an Astrolux A01 . I put mine on a neck lanyard and only took it off when we did a sponge bath.
It is a twisty and has ‘next mode memory’ which is not ideal, but the form factor is great. It is small enough to not be noticed on your neck, works great as a zipper pull / nightlight with a shorter lanyard, and because of the way it is machined, works very well as a ‘mouth mounted’ light. Your lips and teeth can pretty quickly learn to point it where you need the light, and since there is no switch on the end, you don’t worry about getting it covered with drool.
Not having to hunt around in the hammock or backpack in the dark was quite reassuring. When I woke in the night, I always knew where it was - hanging from my neck. AAA batteries (Energizer lithiums) are small, lightweight, ubiquitous, and have sufficient run time in this light when used judiciously as a backup light.
Plenty of us have been low key lobbying for an embiggerated A01 AA version that might only change the UI to do away with the next mode memory, but so far no joy.
Have fun!
I used a Thrunite Ti-3 as my primary light for 20 days on the JMT this past September. I ended up bringing 3 AAA lithium batteries, but never depleted the first and only one installed in the light. It clips to your hat, so works as a headlamp. Total win for a backup light I would say. I primarily used it in moonlight mode, but also in 12 lumen output also. It does not take much light in the back country to see what you are doing.
Hope that helps, and have a great trip, Matt
Olight i3s
Lumintop Tool (comes in AA or AAA)
If you make the switch to AA’s then i would also consider a zebralight for your headlamps. One of their selling points is the efficiency they provide with AA circuits. More runtime=less batts.=less weight
I know weight is a huge factor but IF you have charging capabilities (solar,powerbanks) then the 18650 battery has best common size/capacity ratio out there. They would save you money in the long run too.
Petzl E-lite is a common backup (weighs 27 grams) for thru-hikers but its a headlamp (sort of).
Yep, that was my backup light as well.
I recommend the Thrunite Ti3. It always starts in moonmode so you won’t disturb people in a tent or shelter. Strobe is available but “hidden”. The clip is reversable so it can be used as a headlamp on the brim of a cap.
A big step up is the UltraTac K18. It’s 3 times as bright on a 10440 cell and can also use AAA cells. If you carry a power bank or sometimes go “off trail” you can recharge the 10440.
I own a shoe box full of AAA lights and these are my choices.
Astrolux A01 / Manker Boney is a nice “secure” design. The tube is one machined piece, not even a sealed tailcap or anything, as the battery tube is the tailcap. 
I like the Orcatrch E01, which just got ruined by an alkaleak, ain’t on Amazon anymore, but I contacted OdePro and kinda scored a new one for 9bux (6+3) to replace my original if I can’t drill out the damned alkaleak. Really nice slick design.
Glaree generic AAA lights, got a few for like 5bux a pop, really lightweight, as if the tube is rolled Al foil. It’s not, and it’s a bit sturdier than that, but it just feels really lightweight. Stick an equally light Li cell in there (Energizer or whatnot, not Li-ion), and it’ll practically float away on ya.
Ain’t got, but a Jetbeam µ seems pretty well-received.
All of the above are twisties, nicely sealed against rain, minor dunking, etc.
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Me personally, unless you’re using it as a zipper-pull or something, I’d have another copy of my “main” light as a backup. Or, at least an AA-based light. Jetbeam Jet-I (AA) or Jet-II (16340) are quite nice twisties.
Two is one, one is none…
For reliability I would suggest one with a tail power button. In my experience twistys are unreliable and easy to accidentally turn on.