/diy/ - Do It Yourself

Alright /diy/ I need a lithium ion wizard here.
I've pulled a bunch of 18650s from some dead laptop batteries and I want to try making a battery pack.
Two batteries had skid marks on the control board but the cells were all charged, so I susped that the FETs shat themselves while the cells are all fine. The third one had two dead cells (in parallel).

I'm having a couple of issues though. I'm using an IMAX B6 mini charger to charge them and most of the cells don't seem to want to charge above 4.05-4.1V, and they seem to drop back around 0.05V after a day or so. They don't seem to be losing any more charge after that.
Is this normal for worn cells?

Secondly, I tried discharging two cells (they're still soldered in parallel from when they were in the pack) that were at 4.03V to check the remaining capacity.
>discharge at 1A (so 0.5A each)
>it stops at 96mAh
>"well that was shit"
>check the voltage, it still reads 3.87V
>try discharging at 0.5A
>it stops after another 250mAh, the voltage during discharge was around 3.3-3.4V when I checked (at the start)

So I go off to do something else, come back and check the voltage on these two cells, and it reads 3.8V again. I thought it was just a floating voltage, so I tried shorting them with my multimeter to see if they had any juice left, and promptly burned my finger. They briefly pulled >25A before I disconnected the cable.
Now they're discharging at 0.3A, they've delivered about 100mAh and the cell voltage is stable at 3.51V.

So what the actual fuck is going on here? I thought they had a very high ESR which was limiting my maximum discharge current, but how can that be if they can still pull 25A when shorted?
I don't have much experience with lithium batteries at all so I need someone to hand hold me here for a second.