Hands down, the Opus BT-C3100
Sorry I can’t recommend one for 20700 or 21700 yet.
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I use Nitecore new I4 for 20700. It will do 21700 as well
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Here’s a list of chargers that will (or won’t) do 21700 
There is a gyrfalcon there in the list. Amazing but pricy
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I’m using the Nitecore i8 and they fit fine.
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I read in a few places that people claim Gyrfalcon chargers to be the best of the best, but the prices seem to be in the $60 range for the big one (all-88).
In any case glad to be of assistance
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Also, which ever charger you get, try not to insert the batteries at an angle. The slider barely fits 2x700 and can easily tear the wrapping if you are not super careful (i saw this on a few different ones including my nitecore)
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Will handle 20700 and 21700
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Ok ok… I recommend you charge your batteries with the Opus you just bought! 
Seriously though… The only reason I didn’t comment on the ability of it to do 2x700’s was because I don’t own any to verify with.
I’m glad you got it though, it’s the best charger on the market for the price (and our purposes) IMO!
Mine’s been in use for over 2 years now, and never had a problem. PLUS it’s brought back a couple of batteries that were drained well below their recovery threshold twice in that time!
I’ve been impressed with it, and obviously very happy with the purchase!
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What I love is the ability to measure internal resistance and overall charge. Helps weed out the weak batteries that can be relegated to flashlight use.
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I happened to land on their daily special when they had Sony 40Ts for under $12. I was pretty happy about that. I like their gorilla battery cases as well. Just wish Gorilla would start making cases for 21700’s. I’m diggin the battery life on those.
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Groove! I dropped by the pharmacy and they gave me a bunch of bottles closest to the 21700 size. I offered to pay and they declined the offer. I think they added that to my profile because now most of my refills are coming in that size bottle. Pretty sharp folks.
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You had me on that one. I’ve got two Nitecores, i4 and i8 but they don’t have that ability. I just had to order one 
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Love spending your money sweetheart! In the long run it will save you money. Good investment!
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I am currently testing the Xtar D4 and VC2S and both fit 21700 with no problems. D4 not recommended for charging 3 married batteries, it will charge 1 at 2 amp and the other 2 at 1 amp. Not much to them as well, no option to change the amp rate of charge but 21700 is no problem.
I do like my Hohmtech Hohmbase chargers for the battery doctor feature but 20700 and 21700 are tricky to get to work on them. Have to lift the positive side until it makes contact.
My old efest Blu6 will charge 21700 no prob and has been a workhorse.
If you want to charge really quick the xtar over 4 slim is the fastest I have at 4 amps but only takes 2 batteries and at 4 amps you batteries will degrade quicker. You can change the charge rate to 2, 1 or 0.50 amps with the over 4 slim though.
The Xtar VC4 was my first high end charger and still works great. For being a charger that was out prior to 21700 it actually charges them as well. I have 5 Xtar chargers and they all work with 21700, can’t say the same about other mfg’s like nitecore, there 8 battery charger did not work with all 21700
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Nitecore fit 20700 but they are super tight and hard to get out - i use a xtar vc4 or a golosi s4 for 20700/21700. The Xtar will only fit them in the 2 outer slots the golosi will fit them in any slot.
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That’s what she said 
My VC4 fits 21700 in all the slots but you can’t charge a pair of 21700 in the center slots as the batteries are too wide so they elbow each other out of the slot.
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Always heard good things about the Opus chargers, great choice
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