Richard,
Try to find the small HotLap Timer (GoKart) display.
My hotlap is about 12 years old and has the big display case with the same funtionality as the small one, but it has a 9V battery in the display. It went thru many sand buckets

Formula Ford, F3 and Porsches. These things are pretty well made, I only had to soder it once in 12 years and once the battery was dead

. (thanks Tom T. for the hint I was about to give the Hotlap up but it keeps going and going and going)
The used one sell between $100-$150 and I think a new is about $200 from Dave Motorsports