I doubt it would be a loose battery cable -- either you'd be getting battery power or you wouldn't.
If you had it on high gain, that might definitely explain things. If the mk5's have a sensitivity of 15mv/Pascal (a typical number), with SPLs at 118db (a bit high, but about right), if you then had the 'sax on high gain at about 2:00 (at least 36db of gain?) -- then you'd be asking the 'sax to put out a ~26dbu signal, but it can only put out 20dbu. So you'd be clipping on the output, which would look alot like what you saw.
The OVD lights wouldn't necessarily be lighting up. Over lights can be set up to indicate input overload (too hot of a signal from the mics) or output overload (too much gain, so asking the preamp to put out a hotter signal than it is capable of) -- or both. If the OVD lights are only designed to indicate clipping on the mic input side, they wouldn't light even if you were clipping on the output.