Battery goes down after sitting up.for a few days

There are a few possible causes for your concern. The battery itself could be failed. Even if new. Or there could be a parasitic draw -- causing the battery to run down while away from the vehicle. Read this at this link to learn more -- https://repairpal.com/parasitic-drain-diagnosis Seek guidance at a shop near you - follow this link: https://repairpal.com/auto-repair-near-me#&zipCode=