Could be. Typically a single cell (one of 6) shorted by sulfating will rather quickly (anywhere from a few minutes to a few days) cause the voltage to drop to 5/6 or about 83% or about 10 5V. I'm no expert on lead-acid batteries so I don't know what other causes rhere are for a "dead" cell. I do know that even a bump during mishanding can cause hidden damage.

 

The shop tested the battery and got 12.77V, and my voltmeter reads it at 12.54V, and the battery is from January of this year, so it very unlikely to be a battery problem. I was able to find and test the connector and pins for the BCM and this is what I got: With the battery disconnected, the connector side (the wires to the BCM) gives me 120 Ohms, which is expected because double checking at the OBDII connection it is also 120 Ohms, meaning that the BCM has one of the two terminating resistors. However, when reading the pins on the BCM itself, it is 50 Ohms, when it should be 60. Very odd.

 

alternator?

 

Seems like a connection on the BCM. The interior lights are controlled by the BCM.

 

I would agree if it’s not self discharging. Easy to test for that; leave it disconnected for a couple of days.