Hi, Its my 2nd year with a pool. 65000g with a zodiac duoclear 130. No issues last year but this year the generator keeps going to min and saying add salt. I can get it to start generating again for a while by switching polarity but it only lasts a day at most. I believe the cell is on its last legs. It's about 5 years old based on what the previous owners told me. What causes them to fail? Just want to maximize life out of my new one.