I was going to put one of my 3s in storage mode, when I noticed the voltage was oo low for a 3s, 8.4v, when I connected the balanced lead I saw that one of the cells was at 0.xx volts. I was a bit surprised by that as the lipo is fairly new, about a month and a half. But it seems I got lucky.
My question is, can this be saved as it is ?
You may be able to try, depending on what your charger allows. But be very careful when doing so.
I’ve certainly recovered batteries from such issues.
Another possibility is that you actually have a bad connection on one of the wires!
I see…
How did you do it?
You start charging… slowly…
If the charger won’t let you, then you disconnect the balance plug and try it that way, if necessary choosing a battery technology that doesn’t use a balance port.
You go really slow and keep an eye on it. Check for it getting hot, etc.
You don’t go anywhere near the capacity of the battery and you should regularly check to see if that cell is taking charge.
I suggest once it does that you then stop… see if it holds charge… if it does then you can tentatively try to charge the battery further with the balance lead attached.
Be careful… don’t leave it alone. Make sure none of the cells get hot or overcharge…
Have a way to get the battery to a safe place quickly if something goes awry… You live in a block of flats? That may make this more difficult.
If this looks like it will succeed then the recovery from 0V to just under 3V should be really fast… no more than a minute at most.
As @yith says 
check the wires on your balance connector first
If you have a voltmeter, do you still get 8.4v on the main connector?
Tks for the replies guys.
8.4 was on the main connector. After I plugged the balanced is when I saw that one cell was at 0…
The battery was fully charged before. Should I try to discharge a bit before trying to charge again?
This is a GNB 550mAh lipo, I usually charge at 0.6 amps, going with the process Richard mentioned, should I keep the same amps or lower it more?
Might as well open it up before anything and check if any cables came lose inside… ( On hindsight, if this was the case, the whole thing would not work right bc they are in series)
I’ve tried to recover 0 voltage cells in the passed with no success 
They just puff up and become dangerous so be careful 
Yep, and would you trust it to fly a craft that costs more thana new battery ?
the cells are usually joined together well with thick foil tabs, it’s if a balance wire has come unsoldered you might be lucky 
Would the balanced wire mess up the reading of the main lead?
No…
I’d lower it.
I am pretty sure you have a cell down
Just use a voltmeter across each cell on the balance lead. Do what your charger has done, but do it manually. The charger can get confused.
You will soon see if one cell really is 0V.
Seems like it be more worth trying to make it a 2s rather than trying to bring it back to life…
Is this very common (the dead cell bit)?
He probably does… but I have had chargers get confused.
Reasonably… I have a couple of batteries which I have reduced by one cell.
Measure each cell individually. Each pair of wires.
Don’t measure from ground for all of them… it can produce odd results in some strange cases I’ve had.
Can your charger measure the cell resistance
