Remote's Battery Mystery Solved
In the hope this might help someone else...
After replacing our DirecTV remote's non-rechargeable batteries (2 AA) with brand new rechargeables, the remote would not work. I put the new rechargeables into the charger for an hour and tried them again. Checked positive/negative alignment. Still nothing.
Who knew? I finally realized that non-rechargeables are 1.5 V each, while the rechargeables are 1.2 V. Evidently our remote craves the full 3.0 V and won't work for less!
(Y'all probably KNEW that, but I didn't.)