Error 11 is a stuck accelerator pedal, but I don’t think that is your issue.
Sounds to me like batteries -
Check the voltage of each battery after charging. - you will have to disconnect them, Are all the voltages the same?
Put a voltmeter on the pack and hold the brake pedal and press the gas a little, does the voltage drop off quickly. If so you probably have a bad battery or six.
I am sure the crew here will have some good ideas for testing.