1996 Freightliner - Intermittent Engine Shutdown Light

Yep mines doing it now. It started up fine, ran a while. Next day started up and shutdown. Red shutdown cel light is constantly flashing. Check the diagnostics, Code 46 low ecm power from battery. I’ve had this code for a while. Just never shut me down before. It may or may not be the problem. What has me stumped is usually the dash lights won’t come on when it loses power. This time is different. I’m getting power to the ecm, just not enough. It’s somewhere between the batteries and the 5 pin power plug on ecm.