I believe, there is a way you might accomplish a battery (rechargable) operated (auxillary) tail light. So, if you are determined to proceed with this, here goes. Connect a diode to the yellow wire, connect the diode to a selector switch, connect a terminal of the battery to the selector switch, connect your auxillary taillight to the selector switch. Connect the other side of the battery to ground (any brown wire) The two position selector switch is always connected to the battery and can select the diode or the auxillary light. During the day the switch selects the diode (the charging path) and charges the battery. At night, the switch selects the auxillary light or you can select it only when you stop for a traffic light. I can not predict the extent to which the battery will be charged. A DC current meter in series is required. It depends on the dynamics of the coil and the battery. Be sure the diode is in correctly or the battery could burn something up. Better yet, put 10 ohms in the diode leg to current limit the connection from the battery to your ped lights. Good luck and proceed at your own risk. My legal disclaimer is: I only believe this will work, I am not certain