Rear brake lock up - adjustment?

Hey All,

I was driving home while a) charging a battery booster pack through the 12V outlet, b) stereo cranked up, c) while hypermiling...dash lit up (triangle of death, red (!), ABS, yellow (!). Pulled over, checked 12V aux battery via Display/headlight switch 3x...down to 11.5V. Turned off stereo, unhooked battery pack, continued my journey. Got home, read a pile of codes, reset them, battery now at 12.5V IG on, 14V running. All good.

My concern is that when I stepped on the brakes to bring the car to full stop, the rear brakes completely locked up; I now have two big ruts in my freshly paved driveway. Had it been wet out or during winter, the car would have been out of control.

Is there a way to adjust the rear brakes so in the event of brake system issues i.e. skid control ecu dies, they don't lock up?

Thanks,

FH