I replaced my battery this week with one that had the vent tube on the wrong side. I had to cut a notch in the battery holder and it seemed ok.  Apparently not.  I put the tool cover back on early in the morning and rode to work.  Two days later, I noticed it was gone.

What do I do now?  I can order a replacement, but what do I do about the key, do I have to get the whole mechanism?  A used one seems to have the same problems.  I am not a fabricator at all, but is there a different solution I can take?

I knew I should have parked it and waited to order a big crank  

Ignore it.  Its function is to hide/secure your tools.  If you do not need this function you do not need the part.  This is how an honest Ratbike starts.  (as opposed to the poser ratbikes that are designed to look ratty.)

Did you still have your tools?  Get a small fork or sissybar mounted leather tool bag -- which will allow you to carry mo' better tools.  See!  It's a win-win situation.