I have a BM2 that I have used before on my Kona and now have on my Crosstrek. It monitors the 12V and keep data for the past 30 days which then displays on your phone. It gives you the SOC of the 12V over that time, and most importantly when it is charged. My Kona would periodically check the 12V SOC and charge it from the traction battery if necessary during idle times. That way it could never go flat. I assume the Solterra does the same, but would like to make sure. With the Kona, they actually did a later software update because it wasn't charging enough, and increased the frequency check to about 20 min, I think. In any case it did a good job after that of preventing 12V failures.
Our EVs have a lot of parasitic draw because of all the electronics and communications that are live even when idle. This uses the 12V, and if it is not charged enough there could be a problem.
Even on an ICE car the BM2 is useful, because the OEM batteries can be easily damaged if they are overly discharged and not fully charged immediately after. Short and infrequent trips are esp bad. But if properly monitored and charged externally when necessary they can actually last quite a while. My Crosstrek battery is now over 5 years old and still working fine. Many don't last 3 years. People tend to blame the OEM battery quality, but it is actually the abuse that does it. That includes maintaining SOC and also fluid levels, esp in hot climates.