On iMX6, iMX7 and Vybrid based modules it's possible to use the internal RTC without relying on an external one.
RTC must be battery-powered as described in [this article.
The internal RTC supports a range of around 30 years and this may not be enough for your application, considering that by default Windows CE uses 1/1/2006 as the base date for RTC.
A fix provided in the latest release of iMX6 (1.4), iMX7(1.2b4) and Vybrid(1.6b4) BSPs and images allows you to use the internal RTC overcoming this limitation. This requires a few manual configuration steps.
1. You need to enable this feature in the config block. Set the rtc.useinternal config block parameter to 1 and, if you want to change the range of RTC times, set the rtc.year parameter to the required value (default is 2016). Save and reboot.
2. Remove automatic execution of RTCSync (that relies on external RTC) by adding this entry to your registry and saving it:
This will prevent the execution of the RTCSync tool on your device (executing it without an external RTC connected will slow down boot but should have no other side effect)