My friend Henry Xu of Opus is unfortunately MIA for a very long time I could easily propose the idea to him. 
Oh, I hadn’t thought of OPUS. I’ll try to contact them alongside the others.
I think we have the highest chance of success with Miboxer or SkyRC, since they already have a lot of experience in these fields.
What would the ideal target price be? 39$ for the charger with every non-USB feature and 49$ for the charger with USB features?
I am not a charger expert, but this looks impressive so far! 
Can the charger automatically choose a suitable charging current based on which type of battery is inserted?
(That's the feature that I would be looking for.)
I’d love something like this. Has been much needed as most chargers on the market are severely lacking.
i’m in for this! 
@raccoon city, that is an excellent idea. It would have to be rather conservative however, as to only allow currents based on previous charging measurements or set in by the user.
@Jtm94, yeah, same thing here.
Adjustable charging voltage and low capacity recovery are two things that no charger on the market currently have right now.
@DBSAR, excellent.
BTW, if you want to give suggestions, just do! I want as much community feedback as I can get, and note of course.
Miboxer’s C2-4000 can do ~1A*2 discharge with a noisy ass fan. Get a better fan and run it at half power and I would propose 1A discharge if possible.
It should be easy to use, like using a hobby charger (which has already the features this project aims) but this time having 4 individual bays.
Enable it to keep four cells in trickle charge indefinitely and put a floody LED with a smart (TK) user interface on it — so it becomes a grab-and-go item for those of us in earthquake territory.
@contactcr, no problem. Just upped the discharging current to 700mA. 1A could be possible, but you’d have to limit discharging current to 1A/2 bays to help with heat dissapation.
Also, putting a small aluminium heatsink on these resistors would help a lot.
@hank, that is easy peasy. Just set the charging voltage to 3,9V, and be off with it. Charge it normally up to 4,2V once you need it.
I love the idea of a perfect charger. I have to use a Folomov A1 to charge my Wuben 21700 that is 75.1mm. Could this project somehow ensure that the longest 21700s fit?
Yes, absolutely.
What is the absolute longest 21700 that exists?
Is it that 21700 from Acebeam that uses a buck-boost converter to charge USB devices and charge itself?
I was thinking of something plug-and-play.
The charger recognizes the chemistry and length of the cell being charged, and chooses a suitable charging current.
(I don't know if that's possible.)
That is possible, but is slightly harder and more error prone.
Chemistry is just based on the internal resistance analysis, but it has to be conservative. Currently, the C4-12 that I have likes to go at 3A on my 30Q during automatic charging, while I would prefer 1,5A at max.
Length would be slightly harder, but would require additional hardware.
would be cool if it did it based on length + resistance so high current 18350’s dont get overcharged but still allow like a VTC5A to be fast charged
How about a BLF firmware for the MC3000?
Wouldn’t that cover just about everything you’ve asked for?
Yes, but not in this case.
The MC3000 doesn’t have:
- Support for long 21700 cells.
- USB data out.
- The higher conductivity brass contacts.
And other miscellaneous stuff that I haven’t included.
The design of the MC3000 isn’t also optimal. I prefer the C4-12’s design.
And it’s also rather expensive.
Okay, cell length might not need to play a factor if internal resistance is being analyzed.
I told you I'm not a charger expert. 
definitely watching this one, looks very interesting.
I would refer the option to custom selecting cell chemistry, type, size, and amps-charge rate when required, ( but have a auto 18650 LiIon & AA NiMH as standard automatic with a default charge rate, ( but also customizable. Also woudl be good to have one of the charge Bays adaptable with an output port, (the charger would be great with at least four bays) that output port would have leads for charging wired cells like square LiIon and other packs, large cells like 32650s, (i have 7 of them) and even have the lead-adapter with tiny magnetic positive & negative connectors so they can snap to everything in cell size from a 10180. I know cost may be an issue for that, but a true “universal” charger needs to be able to charge every type of cell at every amp range selected, and connect to them easily. One great single cell charger i really like that can charge nearly every size cell is the Olight mini USB magnetic charger, (I have 5 of them) ( that senses the polarity and charges them, But the only issue its set at one charge rate only.