I bought a 1/2" 18V gun from snap on with the CTC720 charger. I was to understand the batteries would be good for up to 1000 charges, however, the charger itself has failed and the batteries have not been charged more than 500 times. I did a Google search and people are selling these chargers secondhand for spare and repairs. So my question becomes, if they can be repaired, whats the common problem and can parts be purchased? Thanks