MacBook battery sparked when pushing down

I replaced the battery in my MPB a few days ago and the battery so far has been working flawlessly and all was well.

However I felt the batteries moving around a bit, so I took off the back case and decided to apply some pressure to get the adhesive stuck down more. I applied quite a bit of pressure for a minute to each loose cell, and at one point I noticed a very, very small spark at the bottom of the cell when pressing some more. I also did not disconnect the battery when doing this. There was no smell and the mac continued to work afterwards.

Is it likely that I’ve damaged the battery by pressing down on it so hard? I mean, is this a normal reaction for a li-on battery when heavy pressure is applied, or is this indicative of something being broken?