it does not matter how old it is, it matters how many times it is powered on, there is a count that will expire , i have a tool, and was told it has 250 counts, i was also told if i just turn it on, use it and then unplug it and not press the off button, the count will not decrease, this is what i have been doing, but not sure if that advise is true. any way i guess 250 counts should last at least a few years, as the dmc is a pretty good unit, and you can usually fix it without the tool.