Check the voltage at the battery with the car running, if it doesn't get up to around 13.5-14 volts + it's likely the alternator or alternator pulley.
At 115 K miles it could be the alternator or the pulley. My alternator went at about 100K miles.
Here is MOGOLF's alternator pulley check:
First Use a 19 (edited)mm wrench to rotate the tensioner CCW to remove tension on the belt.
Use a popcicle stick (or other non-metal object) to lightly hold the alternator insides from turning. Grasp the pulley, and turn it clockwise (as you face it). If it engages the alternator and turns it, the pulley is good. If it fails to engage and turns but nothing happens on the inside, then it is bad. It should not engage if turned in the opposite direction.
