No need to get your nose close. Use a voltmeter or multimeter (your new best friends). Then check the battery voltage—around 12.6V when off, above 13V when running (with engine on). And, while testing ...

Learn more› By The Deals Team The Deals team hunts for and highlights only the best discounts on picks made by our editorial experts. As Prime Day winds down, we’ve stopped our up-to-the-minute ...