Our pilot units used (2) AAA and we had participants who used them for an entire season without needing to change them. Our RF protocol uses almost no battery energy - so battery consumption relates directly to LED use - the more you are on your brake the faster you need to change the batteries (that said, LEDs are getting both brighter and more efficient all the time). I would expect 2-3 months in average use, perhaps longer. If you are in a parade, a lot less, lol. For the final unit we are considering CR123 batteries which may allow for a daytime running light feature.