After replacing a worn 29 year old tensioner, I made the mistake of having a new one installed that was the 15 dollar plastic type. Bad Idea.
The cheap one cracked right down the middle, and luckily I was able to continue on the road because of my all mechanical diesel engine. After 2 hours like this on the road, the headlights and everything electric were dying because the alternator wasn't turning and the battery completely died.
The next day I lifted the hood to find the root of the problem. and dead battery
So i paid 100 bucks for the genuine piece. It hurts, but would have hurt more being stranded on the side of the road.