FiberBot using Adafruit 8x8

In the book Make: Making Simple Robots, FiberBot a simple e-textile Arduino bot needs:

1. an Adafruit mini 8 x 8 LED single colour matrix with backpack (5V)
2. an Adafruit Gemma 1222
3. a 3 x AAA battery holder with JST connector + batteries to give 4.5V of power

Pimoroni doesn't appear to sell this battery holder. Is there an equivalent? My current holder, with JST, gives 6V which, I assume, is too much for the LED matrix. What battery combo should I get?