My situation - Camper van with a Starter battery grounded to vehicle frame and Camper Auxiliary Battery grounded to vehicle frame (different location). I have the BMV 712 shunt setup so that all Camper Auxiliary battery peripherals are going through the shunt. On the Shunt, +B1 goes to the Camper Auxiliary Battery positive and +B2 goes to the Starer battery positive terminal. I DO NOT have the Starter battery negative attached to the Shunt. I only require reading the voltage of the Starter battery. Here is my problem - When i detach the Camper Auxiliary battery ground from the frame of the vehicle, my BMV high voltage alert goes off as i watch the voltage of the Starter Battery continuously rise (as high as 21v before i returned the ground wire). However, a volt meter attached to the Starter battery shows ZERO increase in voltage. So, the voltage spike seems to only be evident in the BMV monitor itself.
Questions:
1. Why am i seeing voltage spike on the BMV but not an actual voltage spike on the battery?
2. Will i damage anything? (i won't be removing the Auxiliary battery ground very often if at all - i was testing for parasitic drain)