Just Installed BM-2 Battery Monitor and NOCO On Board Charger

The BM2 battery monitor does not have a good way to estimate SOC, as it can’t measure and integrate the current, which gives the charge. The sensor in the car does that.

Chances are that, since the car is always charging the battery when it’s cold, the BM2 battery monitor thinks the full charge is around 13.0 V, since the battery tends to be slightly overcharged because of constant charging.

 

5th Gen EVAP Leak Check Conditions ...

 

I just verified that this is exactly what happens in my Gen 4 Prius Prime PHEV: 5 hours if the engine is cold and 7 hours if it is still warm.

In addition, there is always a small dip at 50 minutes, which I don't know what it is.

23:41 shutoff, 00:31 small dip (unknown), 16:41 big dip (EVAP). Note that this is an AGM battery, so the voltages when the car is off are about 0.25 V higher than with a flooded cell.

You can also see the sub DC–DC converter in the AC charger in action in the first screenshot, between 18:00 and 20:00, keeping the battery at a float voltage of 12.92 V while the AC charger is actively charging the traction battery. The sub DC–DC converter turns off when the traction-battery charging ends. This is the only difference between Gen 4 and Gen 5—the latter does not have a sub DC–DC converter in the AC charger and instead activates the main DC–DC converter during active traction-battery charging.