Following up...
SAM is allowing the battery to discharge to grid under some conditions. This is a bug that we will fix for the next update:
github.com/NREL/ssc/issues/513
Another issue is that the battery discharges faster than it can recharge. I was able to get the lead acid battery to perform more normally by changing the nominal capacity from 15 kWh / 15 kW to 15 kWh / 7.5 kW and changing the dispatch charge/discharge from percentage to 100% to 25%. This reduces cycling on the battery to keep its temperature (and therefore voltage) within a more reasonable range.
Best regards,
Paul.
