Can someone recommend me a compact single bay li-ion charger for travelling? Thank you.
The Olight UC and Nitecore LC10 are as small as it gets. I own and can recommend both. The LC10 works as a power bank but you’ll need USB adapters because the output is USB-Micro.
Other options here if you sort by “Slots”:
https://lygte-info.dk/info/roundCellChargerIndex%20UK.html
The Fenix ARE-D1 is also really good quality IMO.
Thanks, I’ll check them out later.
For traveling I would choose a compact magnetic charger such as https://www.batteryjunction.com/olight-uc.html
You can also find same style unbranded chargers on AliExpress
I bring another flashlight with USB-C charging. Now I have 2 flashlights and 1 is always charging. It’s about the same amount of space.
Travelling? Hands-down, one of the stick-on chargers like…
(The Folomov is apparently discontinued, but similar donks are out there for <10bux.)
The Olight has the advantage of charging Ni-MH cells, although the charging current is “high” for such cells. But most of these chargers do not charge Ni-MHs so the Olight is still a better option 
In case you are searching for Li-Ion only, you can also check :
Trustfire Uc10: Page Not Found - Aliexpress.com
Nitecore LC10: Page Not Found - Aliexpress.com
XTAR ANT MC1 Plus Battery Charger. It’s small, has it’s own travel bag and cost $4-5. Review of Charger Xtar MC1Plus ANT If you need smaller than the Olight UC Universal Magnetic USB Charger. Review of Charger Olight UC
Mmm, but the Folomovs (and probably workalikes) double as a powerbank. The usb part is m/f.
I take along a UM2. It’s a double-slot… but frankly, still small while having a useful display. You do need to have a Micro USB slot power supply capable of delivering 3A. 1A or less and the charger’s display freezes up. If I’m going to stick to mostly 18650 cells, I’ll bring a rechargeable light (Skilhunt H03 w/magnetic charger cable) and have it serve as my charger.
I have that little Olight magnetic one....it's ok, super slow (max 750mAh if the port supports it....if it's a USB 2 port or otherwise hobbled you'll only get 500mAh if you're lucky). With the latter and a 950-ish 14500 cell it still takes an hour and a half or so.
I wanted a little USB powered charger recently as well and got the Xtar SC1 which will do max 2A....however it won't do NiMH and it also won't take AA/14500 cells, which I didn't realize until I received it.
The similar Klarus and Folomov and Keeppower and a couple other chargers had their limitations, too (I wanted 21700 capacity and NiMH). When I looked at the Fenix I could have sworn that it wouldn't fit 21700 but the listing I see now says it will...good option for a quick buy. The Xtar MC1 Plus was only 1A and wouldn't take 21700 I think.
Ended up with the Astrolux MC01 from Banggood and it checks all the boxes and was only $7. I don't know just how "smart" it really is, but it seems to do a good job and the cells end up where they should be. It has a button-selectable current of 0.5A, 1A, or 2A, takes from about 34mm to 77mm in the slot. NiMH is 0.5A only (good, if not slow for some cells). USB micro connector instead of C, plus the 1A type A output if you need to charge something else from a full cell (does have parasitic drain like most so don't store a cell in the charger). Has constant blinking green lights/bars, if that's an annoyance. I didn't see where HKJ or anyone else tested this charger so hopefully it's not actually crap but I've used it a few dozen times over the last couple months, seems like a good all in one single bay. (Also...odd, but it comes in a rather generic printed marketing box. Doesn't say Astrolux anywhere on it but it's printed on the charger).
Edit: just looked on amazon to see if the Astrolux happened to be listed there...nope, but there's an Imren K1 charger that looks identical for around $14, a few different listings for it. Here's one: https://www.amazon.com/dp/B0946JRWP4/
Had I realized the Fenix also checked the boxes I probably would have just gotten that and paid double instead of going to Banggood...
Ahh, you got me there! 
Didn’t know that :person_facepalming:
Look to the Liitokala Lii 100 multi-chem, multi-voltage USB single bay charger with charging rates of 500mA and 1A, or the 202 twin bay charger.
Chris
I’ll second this.
Small, but still has a useful status display, and quality charging, in keeping with Xtar’s brand. Will take unprotected 21700 cells.
Like any good tool, it does the job, simply and effectively.
If it gets left behind somewhere, it was only four bucks.
One of the most satisfying $4 buys I’ve ever made.
The Lii-100 still has not been updated to accommodate 21700 batteries.
Whereas both the Lii-202 and Lii-402 have had their slots updated to be slightly longer so that unprotected 21700 will now fit.
I wonder why they only elongated the Lii-202 and Lii-402 slots, but not the Lii-100 (nor the Lii-S1)…
Maybe they don’t figure that the 21700s are all that popular?
I’ll check both tomorrow with some 50Es, that I have here.
Chris
I bought the Olight UC. Good deal for $10.
Definitely works! Pretty handy little charger. You'll find that on button tops the end you place on the positive will sit crooked...that's fine, and even if you get it carefully positioned flat it will usually kick itself wonky at some point. Sometimes it will give you the red-green blink and if that happens then usually just disconnecting and reconnecting will fix it (same if it doesn't seem to start...take a little bit normally but if it's not going, just redo it).
I read somewhere it doesn’t matter which one I use for positive, correct?
Correct. That's convenient. I think some of the similar ones like the Folomov (maybe?) polarity does matter, but not on this one.