Cars are great to own until a battery light flashes and your headlights start dimming. Running a car always comes with unexpected maintenance, and major parts like the alternator tend to quit at the worst times.
A complete alternator replacement usually runs about $650. You want to negotiate repair costs separately from how you pay for them, then use a zero-interest card window for the balance so a sudden bill does not wreck your monthly budget.
An intro window is a deadline, not free money. If you still have a balance after 18 months, the standard variable interest rate kicks in on whatever amount is left, so set your monthly payments to finish on time.