The ProMaster SM1S Wireless Speedlight Master Transmitter works over a long range (325' 100m) to control a ProMaster 200ST-R Speedlight as a slave flash. It can fire the slave(s) in up to 3 groups with up to 15 slaves per group using features such as TTL exposure control, slow sync. HSS high-speed sync., flash bracketing, exposure compensation, and more. 

The SM1S utilizes an internal Li-Ion, rechargeable battery as its power source. The unit is incredibly efficient and the battery lasts a very long time. Plus, the SM1S can operate while connected to a charger, for times when you need even more run time. OK, wait a minute, let's explore this a bit more. Let's say your SM1S has sat dormant for 6 months and then you decide to use it extensively for a couple of days. Near the end of day-two you suddenly notice its battery is getting low and realize you had never thought about charging it. Perhaps you can take a 2-hour break and plug it into a wall outlet, since that's all it takes to bring the battery back up to 100%. But, maybe that's not a good option. It's cool. You can use the SM1S while it's plugged-in for charging. Maybe having a cord running to a wall outlet is not convenient. No worries! Grab a common power bank (like the one you use for your phone) and simply connect that to the SM1S. You'll be golden! The USB micro-b to USB-A charging cord is included with the SM1S and is s common cord that can be bought at any corner store (in case you forget it at home). In fact, you may already have one or a dozen laying around from other devices.