My battery has... yellow stuff on it? Is that okay?

First off, I should explain my question. My Nexus USB port became loose. I opened it, fixed the port, and then closed it. No charge. I opened it again, this time examining the battery due to the fact the I/O assembly isn't broken. I gave it to my good friend who has a degree in PC engineering, and he said it wouldn't manually charge and to examine it to figure out what's busted. I then cut a slit in the paper concealing the cords... to reveal a circuit board thing. With yellow, sticky juice on it (I can't describe it any other way). I then examined a battery from another Nexus. The yellow stuff wasn't on it. Could this have anything to do with my Nexus not charging? What should be done (he said the positive/negative cords could need resoldered, keep that in mind). I found nothing about this anywhere else, so I can't figure it out. Also: I removed the tape from the battery/ I/O. Could that affect it?