I have a $39 Harbor Freight Auto darkening. It works pretty well but unless the newer ones have changed, the battery isn't replaceable. How long they last depends on how much you use it, but figure about 2 years. I still use the one I have and have no complaints but when the battery dies, I doubt I'll buy any more. I have a Lincoln Auto dark that I paid about $150 for about ten years ago. I have replaced the battery a couple times and it's a nice helmet. I used the HF helmet because I didn't want to scratch the pretty paint when crawling around. Got scratched anyway, but still works well. Bought a Miller Auto dark because it had a larger field of view and was on sale. It usually works well but my son was having problems with it, so he gave it back to me. It seems the the auto. dark blinks or something ever once in a while. Can't remember what he bought to replace the Miller, but he says it's much better. I tried it once, and it was nice. Wish I remembered what it was. I" ll try to remember to ask him. So the point to all my rambling here is that you need to get a good helmet if you want good results and long life. The HF will eventually cost as much over time. When you turn your head sideways to tack, close your eyes and listen.