Kevin,
Paying 19% interest strikes me as a bad idea, period.
Using a credit card and keeping it current should improve your credit score, but running a balance at 19% -- any balance -- strikes me as counterproductive. Better to get the card and treat it like a utility bill, paying the balance in full at the end of each month.
As I understand it, the big effects credit cards can have on your credit score come from three things:
1. (the biggest positive or negative) how quick do you pay, do you miss payments? "Always pay on time" is good; miss payments/pay late is bad.
2. (next biggest negative) amount of balances being run, relative to your income level. Zero is best, bigger is worse.
3. Available credit line. Creditors see this as "how much can he borrow from people other than me." If the number is big, they have a bigger risk,
because there is a greater chance the borrower might overextend, borrowing from everyone and not being able to pay back.
Only the third factor is affected at all positively by running a balance on the credit card. (But #2, more important, is affected negatively.
Creditors will often suggest that you improve your credit by keeping a balance, but be wary. Remember they have a vested interest in keeping you on the hook. Credit card companies make their profits from the interest they receive. They set the rates high because they know lots of people will default and figure that if they get $X from 19% interest payments for just Y months before default, they profit.
Credit card companies aren't in it to improve your credit. They don't want you to repay the principal, ever. They're in it for your interest payments.
I've learned this the hard way. I have balances on my credit cards right now, unfortunately, because of earlier extravagances, balances big enough that I can't pay them all off at once. I keep them current, which keeps me from taking a big hit to my credit score. But I do take hits, both to the credit score, and to my ability to do other things, because my balance is bigger.
Paying 19 percent interest is NEVER a good idea. Pay on time, pay it all on time.
The only time I would advise running a balance is if you get one of those low rate (4 percent or less) "promotional" offers that runs for at least 15 months. And even those are almost never worth it, since the credit card companies have steadily increased the "transaction fees". The bigger the transaction fee, the longer the offer has to hold to be worthwhile to you. Because that transaction fee effectively means a very high "hidden" interest cost: anytime you have to pay a fee up front it gets added to the balance, you're giving up the ability to earn a return on the monies paid until you've paid the balance off.
There might be a small benefit from showing that you can keep a small balance current without it starting to creep up. But any returns on your credit score are going to rapidly diminish. That first few hundred might get you a small jump....but adding to it isn't going to do much if anything, and before long its going to start taking away from the credit score again.
But running any balance at 19 percent as a good idea? Only if you need the money for an operation and the only alternatives are 25%.
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
Romans 12:2 (NKJV)