Car unable to go into ready mode.

It was broad daylight when I did the battery cable disconnect, so I didn't notice any sparks. Keep in mind sparks are mostly likely to be observed when there is a high current draw on the battery (e.g., while attempting to start the car), which was not the case. The danger in what I did is not much different than when you replace the battery in a typical car (that has the battery under the hood).