One of my Makita 18V 1.5Ah failed a few days ago, I m tempted to by knockoff instead of the brand name.

Am I in danger?

Maybe. There's also a good chance you'll get a battery whose actual capacity is not less than what it says on the label. This Project Farm video looks into that question. https://youtu.be/Xf0qqsRMKpM

My friends and I have very mixed results with knockoff Makita batteries. Some work just as well as name brand, others have roughly half the rated capacity and perform much worse in the cold. I’m assuming your use case is light duty since you’re using a 1.5 Ah battery now, so getting a knockoff probably makes sense.

I’ve used knockoff M12 batteries for a while, no real issues. You can get them in larger capacities than the official Milwaukee ones which is my main use for them. I would imagine the Makitas are the same story.

There are a lot of fakes even if you try to buy OEM.