I have “exceptional” mix without a charge card.
no personal loans
no charge cards
DON'T WORK FOR CREDIT CARDS ... MAKE CREDIT CARDS WORK FOR YOU!
Agreed with @Anonymous - a charge card isn't an installment account. The mix bonus comes from revolving and installment accounts, so I would think that the charge card will not give you the extra points.
for credit-mix there are 3 types of account: bank card, revolving account, and installment loan.
a creditcard counts as "bankcard" and "revolving account"
a store card like lowes counts as "revolving account" only.
im pretty sure an amex chargecard counts as "bankcard" and "revolving account"
any kind of installment loan counts as a loan. car, home, or personal.