I found out that CM5 has their own RTC module... today

[vileer]

You will need to find a battery with the MX1.25 ultra-thin connector. Here are some recommendations from the community. HackerGadgets' uConsole Upgrade Kit - adding NVME SSD(PCIe), RJ45 Ethernet and USB 3.0 to your Uconsole - #1005 by proteus