The PETL Lights have CR2 lithium metal batteries with a shelf life of 5 years. Once you replace the CR2 battery most of the shelf brands like Duracell or Energizer have shelf lives of 10 years. Following is an email from a customer related to this question.
“What is the “normal” battery life?? Just curious on this one. I know that ours had to be at least 6 or 7 years old. They had been stored in a Pelican case outside in a trailer. So they were subject to very extreme temps during winter and summer of each year. And EVERY single one of them worked. That was amazing!!”