I gave the battery to an "expert".

He cracked it open and replaced the cells inside.

Total cost was high but not unreasonably high, about 60 euros for the batteries plus fit.

Knowing that one battery costs nearly 20 euros at my local equivalent of Radioshack, it was definitely the best thing to do.

I tried with a flat-head screwdriver but I knew I was going to ruin it. I think he did a pretty good job. I'm going to get it back this week.