That happend to mine they told me the entier wire harness was friend same with the bms under the steering wheel nothing would work just the radio the car wouldent start. I did have to buy a new battery but its been 5 months now I got 10k miles
They change everithing related to the wire harness ecu bms eveything
I woul recomend to go to another dealer man

had the same problem with a friends 2.0L sentra.  Though he was also running 10,000 watts RMS of subs in the trunk.  We removed his system, after his love for the Boom kinda died out, and now is interested in the realm of performance.  We had originally thought that his stock 35 series battery was the culprit.  Which was quicly replaced with a 35 series Red Top Optima battery.  His voltage issues lessened, but were still there.  Either the car would randomly turn off, or his Tach would jump up and down, under load.  It wasnt the battery.  I tested his alt on the car, seemed to be running fine.  14.4V and 110 amps.  Off the car however, 18 volts, 125 amps.  Can we say Regulator Problem.  Also, the fuseable link was an improper size.  Far higher then it should be.  It would have never blown and would have destroyed the battery.  Also noted, the wiring to the starter was a tad small.  Upgrade to 6 or 4 aga wire, and most if not all electrical gremlins will dissapear. Also noted, a big 3 upgrade is a wise investment, due the highly electrical nature of our vehicals.

tried to start the car today and it was dead.  i feel your pain.  i hope it's just the battery and nothing else.  if this car starts having anymore problems i'm sending it to the junkyard and getting a toyota.