The battery can also disconnect/short internally. I had a waverunner try to strand me at Muscamoot this year with a no start, no power to instruments condition. I gave the battery a couple of whacks with my open palm and it started right up. I got home and tried to measure battery voltage. It read zero with no continuity. I gave it a couple more whacks, and it read 11.7.

Do you have a spare test light or volt meter that you can keep in the glove box? If you get another no-start condition, check for voltage across the battery terminals. That will take the harness, etc out of the equation.

Good luck,

Dan

I had a dual set-up battery with side AND top posts fail like that at one of the side posts. I always checked the battery on the top posts because they were easier access and the battery always tested good. Talk about chasing an electical gremlin! Taught me to never assume.

Replace the battery. The battery most likely has an internal fault. No Voltage for lights and radio absolutely indicates that the battery or cable connections are at fault.

Wannabe is absolutely correct. The dealer screwed you. You need to get your $350 back for your ECM and spend $75 on replacing the battery.

For the record, ECM's RARELY go bad, same for harnesses, connectors and other related wiring. The only caveat to that statement is if the car was ever in a serious collision. Then all bets are off as to the condition of those items.

I also agree with the comments about the side terminal batteries. If you can convert the cable ends and battery to a top terminal design, it would be best. It all depends how much room you have between the top of the battery terminals and the hood.

When you get the new battery, double check your charging system and engine/chassis grounds. You should not be up over 14.2 14.5V at RPMS above idle. If so, your alternator could be cooking your battery and messing up a cell or two.

I used to be (and at times still am) an auto mechanic...now I am an engineer.

my girlfriends daughter had a intermittent starting problem mechanics could not find it always said ecu so one day she calls me and its totally daed put jumpers on it still dead trace ground wire which went from battery to body under battery and then fron another spot on fender to the block,

Turns out ground from battery on body end had corroded through but was still in a position to make contact but once in a while would loose contact She had told me once after she slammed hood shut it started Now I know why

replace cable and never had problem again

My grand national did this for 6 months, but I never drove it, so it didn't really bother me sitting in my garage. I could put my charger/starter on it and it would start and go, wound up replacing the battery. My son's Grand Prix GTP did the same thing 2 weeks back also, lights flickered, interior lights would come and go also..........replace the battery and it'll be fixed.