get a new battery
Battery is new and so is alternator
Taking for granted both were installed properly. It is possible a new alternator is bad out of the box or not rebuilt properly, causing the new battery to go dead. Check the voltage of the new battery with the vehicle not running or hooked up for a jump. If less than 12.5 or so volts, either the battery is bad or the alternator is.
Looking for a Used Explorer in your area?
CarGurus has 72,311 nationwide Explorer listings starting at $985.
Search Ford Explorer Questions
Ford Explorer Experts