from my own experiences, cars don't like to have a charge over 14, a high 13 is even better, its like the computers cant function with that much power.
my last truck i went through 3 alts in 3 days, all over charging, truck didn't run right at all, and had the low volt light on the whole time, all tested good at the store, this was autozone to, so if that's where you got yours i feel your pain.