The only way to fix this was to uninstall the update. After going back to 1703 build version, it worked fine again. A few peple online have had similar issues with Medion laptops not working on battery after installing the update.
I don't want to run my machine from the mains all the time, so hope a fix is issued for this soon. I have posted the issue on Windows Feedback Hub.
Has this problem been addressed yet? Is it safe to update to 1709?