while batteries dont get better with age . there is no garrantee new ones will hold charges for very long either. you can get weak or bad cells in new packs.3 days is too long to take a chance.ESV is the only way to check & be sure . make sure you attach it for at least 30 sec to stabilize for surface charges.I hope you cycle your packs once every so often . otherwise you have no way to know if they are wearing out or not .