Too much voltage to headlights?

I installed @crackedback 's headlight relay kit something like a month and a half ago. Worked great, no problems. I had put new headlights on the car just before I installed the new wiring, they were the midlevel parts store ones, sylvania, like 15 bucks each. Went to drive across the state and it turns out both headlights are cooked, brights and low beams on both headlights, not working at all. Bought new ones at the gas station and it all worked again. But about 3 hours down the road, I lose the driver's side low beam. High beam still works and passenger side is still 100%. I looked and I'm getting 14.5-14.8v at the headlight connector when the engine is running and at some rpm. Is it overcharging and killing the headlights, or are the emergency gas station headlights just junk? (they were like 20 bucks each).
Note: one of the boxes from the gas station headlights looked like it had been sitting on the shelf since before I was born, now I'm not that old, but 20 years is pretty old for a headlight.