I hate to say this, but for your safety I feel I should at least suggest... I hope you don't mind and please don't take offense.
If you do not yet know how voltage is affected when batteries are connected in series, playing around with recovered laptop batteries is not a good thing to do.
I can also see from your photo that with both of your batteries, their insulation are a little damaged with patches missing and battery casing exposed. Short circuits can easily occur.
When you connect batteries in series or in parallel, there may be a rush of current from the better cell to the not-as-good cell, Perhaps the "not-as-good" cell may even be a dead cell. Whether the bad one is full dead or merely "not-as-good" but not yet dead, that rush of current is not a good thing. You are playing with fire here.