Cold weather is generally not a problem. Moisture can potentially be a problem depending on camera but it's easy to keep a camera dry even if it's in the cold. But bring a way to keep the camera dry just in case of rain.
Lithium batteries can handle very cold temps (temps in which alkaline batteries would freeze... a Lithium battery will keep going.) However they will work better if warm. So... if you have a spare battery then keep it in an inside (warm) pocket. If you don't have a spare battery then put your battery in an inside (warm) pocket when not shooting.
You probably wont need to worry about the battery... the weather almanac (using Baltimore) says average winter temps are lows of 27ºF and high of 46ºF. I don't think you'll have battery problems factory-original lithium polymer batteries in those temps.
YOU might appreciate a pair of photo gloves. These are gloves in which either the thumb & index fingers can be uncovered to make it easier to operate the camera (or some variation on the design) but covered to keep your fingers warm when not shooting.
Tim Campbell
5D III, 5D IV, 60Da
