I decided to test the 7xF cell NiMH batteries in a realistic way. I charged them fully, attached the Arduino and the LEDs, and I ran a test program adapted from dbu’s LED Globe idea and code. Here’s what the setup looks like:

I expected it to run for about 2 hours, and I hoped for three. Anyway, I put a voltage meter on the power bus, and measured every 15 mins or so. Results in the graph below.

Holy cats. The battery kept 200 LEDs blinking for 477 minutes, nearly 8 hours! So nominal 8.4v batteries supplying 13 Ah are more than enough.  The power curve is nice and flat until it fails, which is excellent.

A couple of observations here. First, the Polulu voltage regulators totally rock, hella efficient. At no point were they even slightly warm to the touch, so nothing wasted as heat. Second, in real use, the LEDs draw way, way less than their rated max current. Third, the giant, ridiculously heavy batteries are more than enough. No Li-Ion polymer for me, at least in this round.