My volvo keyfob had cracked last time I replaced the battery. I stuck it back together with gaffer tape until I had time to repair or replace it. Sugru to the rescue!
It is hard to see but the whole top area is cracked and missing pieces. The white reside is from the tape.
Step 1: Clean Up the Tape Residue With Acetone
Or, if you don't have acetone handy use fingernail polish remover. As a bonus, it smells a little nicer than pure acetone.
If you are going to replace the battery, now is the time to do so, as you will have to cut the Sugru apart next time. Do it now instead of wishing you had done it...
Step 2: Mix the Sugru, and Apply It
knead the Sugru, according to the package directions. I tore a piece off the blob and carefully smeared it into the gap.
Step 3: Smooth Out the Sugru, and Allow to Dry.
Smooth the Sugru into the gap and mold it to fit the contours of the remote.
I did a finish smoothing by adding a little bit of water to my fingers and worked the Sugru.