> 2.3 | Battery Requirements

> Siemens GSM modules support trickle charging and software controlled charging of Lithium Ion and Lithium Polymer batteries. For using the implemented charge control an external charging circuit must be installed within the host application as explained in Section 3.2 or Section 6.2. Furthermore, to ensure proper operation, maximum capacity over a long run and long battery life, the battery needs to be compliant with the specifications listed below:

> • | The Lithium battery must be specified for a maximum charging voltage of 4.2V. Since charging and discharging largely depend on the battery temperature, the battery should include an NTC resistor for battery detection and temperature monitoring. If the NTC is not inside the battery, it must be at least in thermal contact with the battery. Charging will not start if the NTC is not present.

> • | Ensure that the battery incorporates a protection circuit capable of detecting overvoltage (protection against overcharging), undervoltage (protection against deep discharging) and overcurrent. Due to the discharge current profile typical of GSM applications, the circuit must be insensitive to pulsed current.

> • | The internal resistance of the battery and the protection should be as low as possible. It is recommended not to exceed 150mΩ, even under extreme conditions at low temperature. The battery pack should be approved to satisfy the requirements of CE conformity.

> Figure 1 shows the circuit diagram of a typical battery pack design including the protection elements described above.
> Figure 1: Battery pack circuit diagram
> Failure to comply with these specifications might cause

> • | the charging process not to start

> • | premature termination of charging

> • | short battery lifetime or a destroyed battery.

> When a GSM call or a GPRS connection is established, the battery is discharged at a rate determined by the current profile typical of the GSM (GPRS) transmitting and receiving bursts. In normal conditions, the transmit burst current rises up to 2A when the module is transmitting at EGSM 900 / Power Level (PCL) 5. Under worst case conditions, such as antenna mismatch, the transmit burst current might even reach 3A. See also Sections 4 and 5 for more details.

> Table 1: | Specifications of battery packs suitable for use with Siemens GSM modules

> Battery type | Rechargeable Lithium Ion or Lithium Polymer battery
> Nominal voltage | 3.6V / 3.7V
> Capacity | >500mAh
> NTC | 10k Ω ± 5% @ 25°C approx. 5 k Ω @ 45°C approx. 26.2 k Ω @ 0°C B value range: B (25/85) = 3423K to B = 3435K ± 3%
> Overcharge detection voltage | 4.325 ± 0.025V
> Overdischarge detection voltage | 2.4V
> Overdischarge release voltage | 2.6V
> Overcurrent detection | >3A
> Overcurrent detection delay time | 4~16ms
> Short detection delay time | 50µs
> Internal resistance | <130m Ω Note: A maximum internal resistance of 150mΩ should not be exceeded even after 500 cycles and under extreme con ditions.
> Charging temperature | 0° to 45°C
> Discharging temperature | -20° to 60°C