Enphase battery discharge neutral level creeps up over time

I had my Enphase system installed at the end of October and overall works great, but noticed something unusual in the Home Assistant reporting. I tried to set an automation based on the value of the battery discharge sensor, but the ‘neutral’ value keeps increasing over time. Any ideas as to why this might be the case? I can use instead, I guess, the battery charge level, but not sure if I should be concerned about this.