Well, one failure mode with high capacity electrolytics is increased electrical leakage after they sit for long periods uncharged. Now I imagine many newer ones have circuitry to slowly discharge them when not running so charging them and letting them sit with the flash off may not accomplish much. But charging them and keeping them charged for a period of time every so often will help "form" the capacitors. Off the top of my head I can't remember any specific numbers, but probably running a unit up in ready state for 15 or 20 minutes every three to six months or so would help. I used a Canon 188A a couple years back that probably hadn't been run in five years and it was OK. (But a 177A I inherited from my dad was kaput after maybe ten years. Unfortunately, with consumer electronics, there are numerous other possibilities, including corrosion from storing in high humidity that may or may not be avoidable.
The other rule with any battery operated gear is to remove the batteries altogether* when storing the equipment for any length of time. The goop that oozes out of unhappy batteries is pretty nasty.
* (Edit) This assumes removable batteries; some of the rechargeable sealed lead acid or nicad stuff may be more or less permanently installed. Those do tend to die over time, even if unused, no matter what. So that's another "stuff happens" situation.
Last edited by DWThomas; 07-18-2012 at 08:03 PM. Click to view previous post history.
Reason: Clarified statement that lapsed into geek-speak.