I made one almost just like this, I used a 1 1/2 inch under the sink fitting with a screw on end for the housing and a sealed 12v Lead battry. I used two pipe clamps to hold the housing to the bars also.
One thing I would point out is that NiCad and NiMh can be fast charged where LA can not, and you can buy chargers that will charge them with out over charging if you do a little homework on charge rates and delta peak charging of the NiCad and NiMh battries.