Hi Jason and welcome to the best Lexus forum there is.
By new battery on one of your shortlist. Ask the vendor what they mean. It could be that the 12v battery was changed and not the main drive battery.
You should look in the GS section of the forum and search there for known issues (if any)
As for the battery check. Its actually a Hybrid Health check. Yes it's free but only as part of a Lexus service. I forget how much the Hybrid Health check is, if done as a stand alone thing, but £55 rings a bell.
As for the car it's self. One helluva excellent car. You won't be disappointed.