Yongnuo Speedlite Wireless Transmitter YN-E3-RT for Canon Cameras AS ST-E3-RT Power Source: 2 AA/LR6 alkaline batteries Ni-MH batteries (Best with Polaroid AA/LR6 batteries) Wireless flash shooting time: Approx. time: 10 continuous hours ** when using AA/LR6 alkaline batteries Power saving: Power off after 5 min. of idel operation Weight: Approx.110g(transmitter only, excluding batteries) Firmware update: Provided