You cannot insert the battery in the power supply pins for RTC with no power supply in the board.
As for SH7709S, SH7729R, SH7706, SH7720, to supply power only to the power supply pins for RTC, it is necessary to cut power supplies except the power supply pins for RTC after it transits to the state of the hardware standby. As for SH7727 and SH7705, in contrast, do not cut power supplies except the power supply pins for RTC
The procedure is as follows.
1) Start up the CPU in the normal mode. (Please supply power to all the power supply pins.)
2) Set the CA pin to low level.
3) Confirm the STATUS1 pin is set to "L", and STATUS0 pin is set to "H"(transiting to the standby mode).
4) Cut the power supplies except the power supply pins for RTC.
When power supplies except RTC are cut, modules other than RTC are in the state of power OFF. For this time, states of the pins except the pins related to RTC are undefined.