Search this forum for "battery" and start reading.
This one is relevant to the MCF54455, but serves as a check-list for your question:
https://community.freescale.com/message/84628#84628
For the MCF5329, there's no separate power supply pin for the RTC, so there's no way to connect a battery to it.
Having a low power battery-backed RTC inside a micro is surprisingly difficult. I first came across this with the Motorola MPC860. Its "Keep Alive Power" pin drew 1000 to 2000 TIMES more current than the design intent of 10uA. The work around was "use a bigger battery". They never fixed this one in all revisions of the chip.
If you want to use the RTC as the "battery backed clock" then the "battery" as to supply the entire standby power of the whole CPU. This is about 1mA minimum. This is not "coin cell" territory, more like two AA batteries.
> confirm if we loose or not the time when power goes down?
Yes, it gets very loose. If flaps all over the place. You also LOSE it.
If you need a lithium-coin-cell-battery-backed RTC you'll need an external one on a serial bus (I2C, SPI).
Tom
