The radio shack plug number is 274-1532. That is the one I use.I have not fully field trial my 6 volt gel yet but I do expect at least a month. It is a 8 ah battery. I am not letting the voltage go below 5 volts for 2 reasons. 1- pir not stable at 5 v, 2- gel cell if voltage goes too low would not charge back up.