[IamPurple]

I am wondering - where is the scooter getting the temperature reading for the battery so it knows not to charge it when its too cold or hot?

What if I attach an external battery thats, you know, external - it will have a different temperature. I wonder if there might be a situation where one battery is fine, but the other is too cold to charge, but it starts charging both anyway.

Or charges one while not charging the other and getting a huge voltage difference.

[Madyicstik]

usually there is a thermistor (tear drop shaped senson smaller than a grain of rice) tape to the battery. its highly sensitive to temp changes and depending on the programming sends a signal to either close or open a circuit that tells the controller to either charge or not.

[IamPurple]

Yeah, but what about the external battery? All the installation instructions I have seen simply make a Y connection of the power wires that goes to both batteries. And thats it.