7737 Series AC Charger Not Recognized

My Latitude 17 7000 laptop is just under a year old, spends most of its time on my desk plugged into the original Dell charger. Today I noticed that the power indicator in the system trey shows the AC adapters is not plugged it (i.e. I see the battery icon with partial depletion indication, 77% power remaining). I checked the surge protector the AC adapter is plugged in to; its ok.  I unplug the DC connector from the laptop, wait a few seconds, plug it back in.  Power indicator in the system trey momentarily shows the AC adapter symbol and then reverts to indication of no AC adapter connection. I checked the voltage potential at the AC adapter's DC connector and verify 18.5 vdc with Fluke 8060A DVM.  It appears the AC adapter is working correctly.

While typing this post the power indicator in the system trey now indicates connection to the AC adapter; everything appears normal. I would estimate this happened around 75% power remaining.

Perhaps the system periodically allows the battery to discharge to a 75% state for battery health?

Rick