I will try to charge it to know if it's still working or not. But I was just thinking, all new batteries in the stores which are for sale, do the sellers regularly monitor the status of those batteries? They are brand new but may already be old.
I am using two batteries for my Phantom 3 Advanced when I fly my drone and I have a brand new unused spare battery for future use or sale. This new unused battery is being stored for almost 3 years now. Is this bad? I am afraid that if I regularly charge/discharge it like what I've been doing...