[Q] Robot with dual batteries and relay for 2nd battery

The relay needs current flow to turn on. With 3V you won't get that current flow, so its not likely to work.
The resistor between arduino & base limits the current flow out of the arduino - try a lower value.

"I can if test it with a 5v source to the transistor and that works, but not from the 5v on the Arduino pin...."
What does this mean?