Hoover FM216LI cordless vacuum refuses to charge

[CapLeaker]

Check QC1 and D13. QC1 = AO4459 P-channel (so it is negative) mosfet with a body diode. Look at the gate drive. If there is no gate drive, the mosfet wont do anything. It is configured as a on/ off switch.
Plug the charger in and measure the voltage coming in and going out of this mosfet.

[flat-earther]

I doubt the resistor is the cause. Resistor marking 683 = 68k ohm.
Did you verify the external power supply actually delivering 26VDC to the BMS board? Just to rule out any chance as a PSU issue. Look at that resistor I circled, it looks like it has a hole in it.

Thanks.
My bad, that white is residue from when I cleaned the board with alcohol and didn't dry it well. I wiped it clean now, here's some new photos.

That resistor you circled measures 0.0 Ohms so it's okay.

I have labeled the wires connected to the board so it's clear what each is for:


Measuring the charger plug output without connected to the vacuum, it is 27.50V, a bit higher than labeled, I assume that's fine and since it's not under load.

[CapLeaker]

I doubt the resistor is the cause. Resistor marking 683 = 68k ohm.
Did you verify the external power supply actually delivering 26VDC to the BMS board? Just to rule out any chance as a PSU issue. Look at that resistor I circled, it looks like it has a hole in it.

[flat-earther]

I have a Hoover FM216LI cordless vacuum which isn't charging its internal battery.

I opened up the unit, and it has 6x Samsung ICR18650-22P cells connected in series.
5 cells were at about 3.3-3.1V. one was at 2.4V, so I assumed this cell was bad that's why the vacuum wasn't charging so I replaced it with another 18650, but after that the problem still persists, the vacuum turns on a bit and then cuts out since the batteries are empty.

So I think the over discharged battery wasn't the culprit, it was a symptom of the unit not being able to charge its batteries.

The charger is an external AC to 26VDC charger with a barrel plug.

When I opened the vacuum I noticed that the PCB that controls everything had a lot of dust buildup on it, (I already cleaned it and didn't take photos of the dust).

This is the PCB after cleaning:


When I was doing some probing on the board, one of the 0603 68K resistors near the power switch (this area had a lot of dust buildup) didn't give any reading and then I noticed that the solder joints of that resistor crumbled from my sharp probe tips, what does that mean?:

After repeated probing of the resistor I managed once to get a 68kOhm reading measuring right on the resistor, but there was infinite resistance between the resistor and the transistor marked S3 even though they should be connected through a trace. (the other side of the resistor connected through a trace to the nearby 01C resistor had continuity)
So I tried to reflow one side of the resistor with a soldering iron but that didn't help and after probing it some more the resistor just detached from the PCB completely, and after that I saw that the problematic pad on the PCB was in rough shape, but I managed to somewhat revive it with solder and wick:


Anyway, now I fried that resistor so I need a new one.
Do you guys think that resistor was the culprit of not charging? I wonder whether the charging will work again if I replace that resistor.

Additional photos:

PCB markings:
AS-8206BPL2 21.6V
LA-PABS-8206-A2
This vacuum is designed such that the handheld unit detaches from the main body used for floor cleaning.
I noticed there is a vacuum from another brand that looks physically similar, Rowenta Dual Force RH6751WO