This weekend I verified I can run my new 250-light strand sufficiently from batteries. I used 8 D-cells in a series-parallel configuration for 6V at high current. My conclusion: if I run the strand at a maximum of 1/4 of total brightness, I can run off 8 D-cells with no problem. Brighter than that just draws too much current. Even at 1/4 brightness as seen in the video below, if I turn on all 250 LEDs to #404040 white, it draws 2.8A at 6V, or nearly 17W.
I also wrote a few 10-line functions to do fun things with the lights. I’m pretty convinced I won’t have trouble clocking animation frames into the strand based on these tests.