As many failures I get with reman denso units from napa both alternators and starters. I'd bet on just bad luck and I'll be forking over the coin for a new unit given availability. One thing to check though after multiple failures is the charging/starting harness and engine/chassis grounds via simple voltage drop test, this can cause both battery or alternator failure. Make sure you're in spec I rarely see more than 15mV of drop on either side though most manufacturers spec out much higher.