Siemens TC37 Module At Command Reference page 150

AT Command Set
Unsolicited result code
^SBC: Undervoltage
The message will be reported, for example, when you attempt to set up a call
while the voltage is close to the critical limit and further power loss is caused
during the transmit burst. To remind you that the battery needs to be charged
soon, the URC appears several times before the module switches off. In this
case, the battery capacity is still sufficient to set up a short call.
When the module is in IDLE mode it takes typically one minute to deregister from
the network and to switch off.
Reference Note
· If Multiplex mode is active, any virtual channel can be used to enter the write
Siemens
· The URC "SYSSTART CHARGE-ONLY MODE" is indicated automatically
Table 9: Summary of AT commands available in Charge-only and Alarm mode
AT command Use
AT+CALA Set alarm time
AT+CCLK Set date and time of RTC
AT^SBC Monitor charging process
Note: While charging is in progress, no battery parameters are available. To query
the battery capacity disconnect the charger. If the charger connects externally to
the host device no charging parameters are transferred to the module. In this
case, the command cannot be used.
AT^SCTM Query temperature of GSM engine, enable or disable URCs
AT^SMSO Power down GSM engine
TC3X_ATC_01_V04.00
command and to specify <current>. The undervoltage URC, however, appears
simultaneously on all three channels.
when the engine enters this mode (except when autobauding is active). Unlike
the undervoltage URC, it cannot be disabled or enabled by the user.
Page 150 of 204 29.05.2002