Hello, I've an UDOO Quad with UDOObuntu installed within. I would to enable the rtc, so I've bought a button battery with the connector. When the udoo is unplugged from the power source i've connected the rtc battery to "ext bat" connector, then I've powered the board. After the clock synchronization with online server (sudo ntpdate) the clock is updated but after i have halted and restarted the board the date command returns the original date: 1970. What's the problem? Thanks!