RTC coin battery is integrated in a few models of M3 SKY. The coin battery is used to keep the device alive while changing the main battery. By ‘alive’, we mean the device does not lose any information stored in the device including the time information. However, the device will go to sleep mode.
A fully charged RTC coin will keep the device alive for around 5 minutes. If the main battery is detached for longer than 5 minutes, the time information is lost.
Another scenario that the time information is lost is that when the PDA is completely powered off (turning off the device by pressing the power button for 10 seconds) for longer than 5 minutes. This is because when the device is completely powered off, the RTC coin battery is working to keep the time information and after 5 minutes, it is fully discharged and all the unsaved information will be lost.
To prevent RTC reset, DO NOT power off the device by pressing the power button for 10 seconds (except in the case of special event such as upgrading OS or clean boot) or detach the main battery from the device and leave the device for a long time. Current in the RTC coin battery is flowing when the device is completely powered off and it may result in RTC information loss. If you must detach the main battery for whatever reasons, please place the device on the cradle.
To charge the coin battery, the main battery must be attached to the device AND the device is switched on. If the PDA is not switched on, the coin battery is not charging even if the main battery is attached. When a fully charged main battery is attached to the device, it will take approximately 20 minutes to charge the coin battery.
