not big deal,careless,3 times are enough for 13 balls

3 time is enough for 13 balls:

1)abcde fghij if balance,we can get one from klm.not balance(left W)
2)aklm fbcd taking off ej if balance we can get one from ej if left W bad one in af,also can get it.If left L,one weight one is in bcd,we can get weight.