The DKB Insider uses the Dallas Semiconductor DS1216 RTC chip. I looked it up, and found that it has an embedded lithium battery. Pretty cool that it kept the clock running all this time.
BTW, that chip was obviously in production prior to 1987, which is when DKB released the Insider board, more than four years before Sony released the first commercially available lithium ion battery. That's pretty cutting edge to put a chip into production that uses a battery design that is still mostly theoretical.
DKB products were always first rate, so it's not surprising that they would pick a good RTC chip. I just wish Microbotics would have used it as well.
https://pdfserv.maximintegrated.com/en/ ... S1216H.pdf