Clock problem

[MST]

I bought a Honda Jazz hybrid in September, and am very pleased with it. But whenever there is an overnight hard frost, the clock loses about 20+ minutes. Several nights were frosty recently, and it lost 50 minutes. The service manager at the dealership hasn’t heard of this happening, an I wonder if you have, or can offer any advice. There don’t seem to be any other battery- related effects. I don’t have satnav, and don’t use internet or smartphone connections, but my screen is set to show the date and time.