okay to reuse battery with some peeled tape?

I would try using some 3M 5mm Double Sided Tape to put back the track pad cover & also the covers on the battery cells as these absolutely need to be covered, be sure to put the tape in the exact same areas that it was in originally, leaving no gaps around the edges. As for trying to get to the track pads screws without 1st removing the battery was a bit of a risky move as you have just discovered. It is quite easy to pierce the batteries cells, which would seriously damage the battery rendering it useless and dangerous to use again. It could also cause a shorted circuit on the logic board which isn't good news. Regarding the creases in the batteries cells, this is likely due to age? I have seen it many times and I have even seen it present on new batteries, as long as the cells are not swollen up or leaking then it should still be OK. After you have got it all nicely put back together, install coconutBattery and check the batteries status while charging it to see it's actual condition. Good Luck!