Wavecom GR64 GSM/GPRS Integrator's Manual page 80

In the backup condition the RTC block will function to as low as 1.1V on the VRTC
pin. The RTC draws 10µA typically during powered backup (15µA max).
Figure 5.20 1 shows the VRTC connectivity arrangement.
Figure 29: VRTC connection
TIP
GR64 Integrators Manual
Page: 80/104
Recommended button cell to use is Seiko TS414H. This is a lead-free,
reflowable SMT Lithium battery with a nominal voltage of 1.5V.
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