Okay, since you're a DIYer, check out some tool battery teardown videos. Those are basically the same as bicycle batteries but on a smaller scale. If anything, bike batteries will generally be easier to work on because they tend to be screwed together rather than glued. Safety with high current will the key factor you want to learn, e.g. use non-conductive tools as appropriate. Regarding that damaged clip, my first instinct is that it should be a simple replacement. Should be a matter of soldering in a replacement connector and securing it in the slot. Make sure the battery receiver is in good shape, i.e. if the mount on the bike is damaged, this will just happen again.