the battery of mobile phone was damaged

Two years ago , I bought my third cell phone with two batteries. One is the original lithium battery, the other is also a lithium just as a gift attaching the first one.  I just used the one as gift,   because I have no need to use two at the same time.  one year late , I want to have a try with the other ,do you know what happened ? the battery has been destroyed by itself. I had not touched it any more since I got it in the shop .“why do you know it’s been damaged?”you maybe confuse. For it can not be charged. It’s so unfortunate. I really feel a little sad. Why didn’t i use the two together? now I tell it to you to avoid this happen again in your life!