severe battery drain on ios5.7

I am experiencing sudden battery drain on apple watches (v7 and XE) since updating to ios 15.7. Both are linked to iphone13 pro's . At first the watches would not charge or charged imperceptibly slowly (although they displayed green). Once i updated both iphones to 15.7 this resolved but the battery drin is still happening at rate of about 15% per hour with minimal use.

I have unpaired/re-paired to no avail

Is this a known issue ?