BSI

Battery Size Indicator ( or Battery Status Indicator or Battery System Indicator )

Mobile phones use BSI to identify the type and size of the used battery. This is needed to determine the current and the voltage of the charging.

It is connected to resistor to GND. The phone measures the resistance of the BSI - GND connectors, and it can determine which kind of battery is in the phone.

Nokia NiMH batteries:

• BMC-2 640mAH 3.3 kOhm
• BMC-3 900mAH 5.6 kOhm

Nokia Li-Ion batteries:

• BLB-2 650 mAH 68 kOhm
• BLC-2 900 mAH 75 kOhm

There are some mobile phones, which has shorter BSI pin. It is because when the battery is being removed when the phone is turned on, the BSI circuit interrupts first, which tells the processor to shut down all communication to prevent damage.