I just use an Xtar SP-1 charger/power bank. Single cell with micro in/USB cord out. Uses any cell over 2500mAHR capacity.
Miller ML-102 v8 or newer are good single 18650 powerbank/charger, but they only accept unprotected cells. It can handle up to 1.5A output with peak efficiency around 80% which is decent for single cell.
Although I would recommend getting a dedicated compact charger and a separated powerbank, I used to have a ML-102 in my car but realized it was not convenient having to charge it for almost 5 hours just to get 1.5 hour of operation. Since I do short commutes 5 hours of charge time equals to a whole week of driving just to fully charge 1 single cell.
Tomo “DIY powerbanks” have been proven to be very inefficient and unreliable, some people reporting different LVP for each of the cells. And they are not cheap either…
If you don’t mind building one yourself there are some high efficiency conversion boards, just add your own 18650 battery holder and charging module:
innogie alien 13400
used 3350 cells
Thanks for the spam.
Marked.
We like our Blitzwolf, and when MicroCenter had the Tplink 10400 on sale gifted one to a happy getter.
Easy open, means not water proof. Lions should be happy with long intervals in charging.
I’m currently using a rock 8000mAh powerbank. Comes with a nice feature of a variable dimmable floodlight 
I love it so far…
I have 3 tomo v8 power banks and have the new one the t4 on the way. Only had a issus with one. The soshine version. But imr exchanged it with no hassles. I take one to work everyday and leave two with my wife. The only complaint I really have is the 1 amp input for charging. But usually take the cells out and charge in my opus charger. For $12 I can’t complain about it. Easy to swap cells in and out if don’t have the time to charge them. With Panasonic 18650b I can charge my phone about 3 1/2 times phone has a 3000mah battery
Never heard of any battery balancing issues. Each slot is independent its not a series arrangement so there isn’t any balancing charging going on. Its a charger as well. I used it to charge my vape batteries and my edc while my daughter was being born in the hospital. Was easier to just bring it and use it as a power bank and charge the few cells I needed with me
Even with discharging it keeps the voltage the same. Even with different mah batteries. Like a 2000 next to a 3500. If I pull them half way down on the battery bar. All 4 batteries will be 3.8 and all 4 batteries are different brands when my wife changes them out. When I put them in the opus all the same voltages across all 4 bays
Have a look at Thrunite C2, there will be a new version (which is fixed so that it also works with low power devices) in around one month.
I like that the battery is changeable but sits protected inside the powerbank. So it can double as a charger for 18650 cells. Also, high charge and discharge current.
If you just need a lower power bank, i’d go for this RavPower 6700mAh one unless you insist on 18650 replaceable. I have got it on sale for around $12 and it’s size/shape/weight and features are the best for < 8A backup.
Thanks… I may pick up one of the new Tomo’s and the Thrunite’s for when a small one is needed.
I appreciate the input.
Matt
I have two ELE-Power Thunder 16,000 chargers. LG electronics. Uses Qualcomm 3.0 for charging input and output. The tests I ran (with help from Will34) turned out to be around 85% efficient. Not removable cells, but this thing is nice in the 34 dollar range.
The famous TOMO DIY… I bought one some time ago when it was on sale on GB, while it is easy to use and convenient if you have lots of 18650s lying around!
I have tons of 18650’s and would like to cycle through them and not just put them in a light to run them dead and charge them… although that is fun also!
My tomo 4 cell is great!
I got one of the 2 cell Tomo units. It was really stiff to remove the cover and the second time I opened it I cracked the LCD display. Needless to say I was disappointed. There don’t seem to be any good multi-cell powerbanks with replaceable cells.
I have a TOMO 4-cell one too.
It doesn’t shut off at low current loads, which is nice.
It’s rather big though…
These are said to be good too:
Nice looking slim design.
+1
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how large do you want to go?
I saw a case and electronics for $17 the other day, with space for up to 10 x 18650 cells in parallel (buyer was supposed to add)
I was like, “hmm, maybe a solar panel and 10 protected panasonics 3400 could make this a nice set, keep it in mind and when time comes talk about it on BLF 
”
Xiaomi Mi power bank 10400mAh and 10000mAh are also good (non slim version). Just make sure to get the genuine one as there’s so many fake Mi powerbank out there. The fake ones are definitely crap. Can’t even fully charge an iPhone 5S.
I have stayed away from them because of fakes… I would not know a real one for sure unless it bit me on the butt. I would hate to wait on shipping for a fake that I would have the wait to return.