Battery or solenoid issue?

1992 club car DS gas powered. Was running fine then quit. Installed a USB port with a voltage reading on it months ago and it reads 11.6 before trying to step on pedal, then drops way down. I know it should read 12.6 before acceleration. Should it drop way down, like 5.6 or something or is that symptomatic off a battery or solenoid issue? Car won't go. Thanks!!