I was going to say battery until you said it stalled on the highway. I'd now bet it's the alternator. If you have a battery tender, charge the battery up overnight. Check the voltage with a voltmeter the next morning. I would expect to see 12.5 to 12.7 volts. Then start the car and measure the voltage at the jumper posts while running. Keep the voltmeter leads away from the fan. The alternator should be able to run the voltage up to around 14.3 volts. If not I'd first have a shop run a load test on the battery. If the battery shows good, check the alternator.
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