I am working on a project for which I needed large capacity rechargeable batteries. I decided to salvage cells from two old HP batteries I had. The batteries were in 3S2P configuration. One of the battery pack had LG S2 18650 cells (Pink) and the other one had LG S3 18650 cells (Blue).
I cut out the series connection, and this left me with pairs of two cells connected in parallel. Each pair had a voltage of around 2 V. I charged one of the pairs with an old cellphone, since I did not have a 18650 charger. As soon as I connected the charger, the voltage instantly went up to ~2.7 V, and stayed there even If I disconnected the charger. At 4.08 V, the cellphone said the battery was full, even though it should have charged up to 4.2 V. I disconnected the charger and left the battery for 20hrs. After 20hrs, I checked the voltage and it was at 4.02 V, a loss of 0.06 V.
I have read that if 18650 cells are losing voltage while not connected, they are no longer worth being used. Should I toss these cells out? Is it possible that the cells give higher voltage right after being disconnected from charger and later settle down? And lastly, were the cells discharged down to 2 V or 2.7V when I took them out of the pack?
I have found that by the time laptop batteries are being scrapped, they are typically not in good working order (bad cells) , and many of the cells don't have built-in protection. It sounds like you've got a batch of bad batteries - which is hardly surprising; consider the laptops you've owned, how many of them had working battery by the time you were done with it? I don't think I've ever thrown out a laptop before it's battery crapped out and wouldn't hold a charge.
I just buy third-rate cheap 18650's on ebay - the capacity is about the same as you expect from old laptop batteries, but they've usually got the short circuit protection, which makes playing with them a lot less scary.
I had also taken the batteries out from my old HP 540 laptop. The voltage of an individual battery is about 3.6V. And I charge them with TP4056 IC, a cheap charge IC for Li-on battery. All going as normal, but the battery capacity is very low. With 2 batteries, my RC car almost drains out for running 10 - 15 minutes.
Your batteries after charged with 2.7V is still below dead point (3.7V) and from the old laptop. So they are not good as expected and should not be used to prevent the wasted time with them.