If they are the brand labelled "Shop Lights"? I bought a bunch (14)of these from Home Depot. 100% failure of the ballast units in a very short time. Some didn't last long enough for me to put the ladder away. When I complained the source sent me a second set of 14. Guess what?? I now have completed the exchange of those ballast units also. This is for a lighting system that parallels another similar unit that was installed in 1973 and the ballasts in those units are original. Voltage checks show the same voltage being supplied to both sets.
Stu