I know the warranty is normally 6 months for the battery, does having Refresh extend that ?

Hi Brad, the warranty period of Spark battery is 6 Months and Charge Cycle less than 200 Times and cannot be extended.
DJI Care Refresh is available for the whole kit including he aircraft, gimbal, camera, battery and propellers, which is valid for 12 months and offers up to two full replacements at additional charge if accidental damage occurs to your product during normal use.
Pleas let me know if there is further query.