I would like a switch to seamlessly swap batteries between an experiment and a charger. Here is the description of the switch I am looking for. Originally I1 is connected to O1, I2 to O2 and so on. On turning the switch these things should happen in order: 1.) I3 and I4 are disconnected from O3 and O4 (battery 2 taken of charger) 2.) I3 and I4 are connected to O1 and O2 in parallel to I1 and I2 (make before break) 3.) I1 and I2 are disconnected from O1 and O2 (experiment is now on battery 2) 4.) I1 and I2 are connected to O3 and O4 (attaching battery 1 to charger) Where can I buy it? is there a name for this? Is there a company that produces "programmable" switches?