I had the card about 3 months in my Galaxy S 4 and then it suddenly went into a read only mode. All the data was still there and I was able to copy it all from the card but could not write or format the card. I searched the internet high and low for a solution and then finally contacted Sandisk support. After explaining my problem, they said it will need to be replaced and it would be covered under warranty. The replacement process took about two weeks, they paid for return shipping. I now have the 2nd card and have had it running for about 2 weeks now.We'll see if I just happened to get a bad one or if they all are of questionable quality.