That CC watt meter can only count current in one direction. There is a source side, and a load side, so while it can be left in one direction if only counting current from charge controller into fuse block/ battery, if it were between battery and fuse block it could count only current wither going into the battery, or coming out of the battery but not both at once.
They use a hall effect sensor to count the current.
The solution is to get two meters. and have one oriented in each direction and do some math.
I have this one and it is a wonderful tool:
http://www.amazon.com/High-Precisio...9-9101462?ie=UTF8&refRID=1KYXCE1YA6XXT6J98X3Q.
However it is not accurate at loads under 0.8 amps, and it will not read currents under 0.2 amps. The less the load under 0.8 amps the more inaccurate it is. Also while it says 130 amps, the leads are only 12 awg aluminum wire. The meter heats up and reads higher voltage when passing 25 amps, and the higher voltage throws out the watt measurements. Heat = resistance= wasted power. Also mine resets back to zero once 64 amp hours is reached.
The great thing about the clamp on meter, is that the circuit does not need to be opened up to test the current flowing.
I have found My Sears clamp on meter reads very closely with my shunted meter, and other digital multimeters, including my friend's Fluke meter, which is a top of the line tool.