Powered by an Extreme Li-Ion Battery Fast recycle time of 1.5 sec (4x faster than AA power) Up to 600 shots at full power Up to 1000 shots at 1/2 power Built-in 2.4GHz wireless receiver & transmitter Unique wireless connectivity High performance 60GN at ISO 100 200mm TTL Manual & Multi Modes Firmware update via integrated USB Kit Includes: 2 x MODUS 600RT MK II Speedlights Viper TTL Transmitter 2 x HLX-MD1 Extreme Batteries USB powered MD1 MK II Ultra-compact Charger USB cable