I think he meant that the box worked for 20 years, but not on the same batteries...
I'm guessing it used bulbs that eventually burned out. If you still have it, open it up and see what lurks within.
It could have been as simple as using 9V Christmas bulbs (or something close to that voltage, unless they were wired in series), and using blinker bulbs to make them flash.
You can get LEDs with flasher chips built in. They don't all flash at exactly the same rate, so if you wire up a bunch of them you can get a random flashing pattern. Or you can use 555 timers, or logic gates, or even a microcontroller.