According to Dinotte the light will go for 12 hours in slow pulse mode, and 6 hours in rapid pulse or strobe mode. If you leave it on continuously it lasts 2.5 hours at full power, 5 hours at 50% and 24 hours at 10%. I will likely only use it in the daytime and in blinking mode, so battery life should not be an issue for me. If you have serious battery needs they also make a 4 cell battery that doubles those numbers, but it's bigger and heavier.