Do capacitors automatically release their energy over time?
Discharge the capacitors yourself.  This is a common procedure.  There is even a tool for that, although you can make an improvised one.

  from this post.  Good discussion there too.

Well-designed high voltage circuits have bleed resistors for discharging high voltage capacitors.

Real (as opposed to ideal) capacitor has leakage resistance.  It can be viewed as a large resistance in parallel with capacitor.  There is a leakage current, which could be on the order of 1uA in large electrolytic capacitors.

 from AllAboutCircuits