battery – MBP Pro Retina 2015 of opportunity lost 300 mAh of its total carrying capacity in three months

Last February, I purchased a second-hand MBP Retina 2015, featuring 251 battery cycles and a full load capacity of 8440 mAh. After almost three months, I had the impression that the life of the battery had decreased a little and I was shocked to see in the system information that the total load capacity had dropped from 8440 mAh to 8119 mAh.

I would add that I added 8 battery cycles, but other than that, I used it mostly plugged.

Is there a best practice to avoid this situation?