My battery died a few weeks ago, and AAA came out to replace it. They replaced it with a 51R-series battery.

Today, I change a dead headlight, and when I go to put the support rod back and shut the hood, the rod won't lie flat. The positive post on the battery was in the way. The mechanic at AutoZone said that the 51R was incorrect, that it should be a 51-series. We switched it out, and the rod lay correctly.

I'm looking online to see which battery should ACTUALLY be in the car. Is it possible that the 51R was correct, and that it was just installed backwards? Is it dangerous to be driving with a 51 installed?