hey mate. if your alternator is overcharging for example 15volts and over it could be spiking the computer and the system is shutting down because of it saving the components in your power steering. charge rate for all vehicles should be no lower then 13.5v and 14.8v. some of these problems i've seem through my workshop are caused from an intermitted charging fault. the battery wont cause the problem as it is only a storage device, once the vehicle is running the alt runs the vehicle, not the battery. hope the helps.