A secondary backup battery is integrated in all M3 SKY terminals. The secondary battery is used to keep the time and date information while changing the main battery. However, its functionality varies according to its model and the version of main board.
In early models of MC-7XXXS, a small real time coin battery was included as shown on the below left picture.
<Old Version> <New Version>
Left figure shows integrated (soldered) RTC coin battery and the right figure shows a detachable backup battery.
In main boards v1.1 (MC-71XXS), v2.1 and v2.2 (MC-75XX/77XXS), the coin battery is charged through system power. Hence, if the terminal is turned off by pressing the power button for 10 seconds, the system stops operating and consequently the coin battery is not working. Therefore, the RTC is reset.
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. Moreover, placing the turned off terminal on the cradle will NOT charge the coin battery.
To prevent RTC reset, you must not turn off the terminal by pressing the power button for 10 seconds.
In main board v1.2 (MC-71XXS), the coin battery is charged through the main battery and it follows the main battery level. Hence, turning off the terminal by pressing the power button for 10 seconds will not reset the time information. But leaving the device at off state for longer than 5 minutes will reset RTC and GPS data because a fully charged coin battery is only able to keep RTC and GPS data for 5 minutes. This also implies that stored data will reset if the main battery is detached for longer than 5 minutes.
As improvement of the backup battery system is necessary, M3 Mobile re-designed the backup battery system and it has been applied to the terminal when M3 Mobile adopted new Summit WLAN module. Below table describes the key differences between the previous M3 SKY terminals and M3 SKY terminals with the new backup battery system.
