Structure of the lithium ion battery

The nominal voltage of the lithium ion battery is 13.2 volts.

4 battery cells are found in the battery housing.

The lithium ion battery features an integrated battery electronics module that is connected to the Digital Engine Electronics (DME) by the local interconnect network bus. The battery electronics module transmits the status of the lithium ion battery to the DME control unit.

NOTE: For faults on the local interconnect network bus, a "Diagnosis on Local Interconnect Network Bus" help document is available in ISTA.

The battery electronics module monitors the voltage of the battery cells and equalizes its state of charge. It also monitors the temperature of the battery cells.

Battery isolating switch

A disconnect switch is located in the battery, which can switch-off the battery for protection. The voltage at the battery terminals cannot be measured when switched off. This means that if voltage can no longer be measured at the battery terminals, the battery is not necessarily faulty.

Behavior of the battery isolating switch during fault statuses:

Fault status	Condition for reactivation
Overvoltage	Overvoltage is no longer applied. Voltage at the battery terminals less than 14 volts.
Undervoltage (protection from total discharge)	Applying a voltage greater than 10 volts at the battery terminals (e.g. with a charger).
Operation at high temperature	Temperature of the battery is less than 80 °C.
Short circuit	Applying a voltage greater than 10 volts at the battery terminals (e.g. with a charger).

For the reactivation of the battery isolating switch, it is necessary to apply voltage on the battery terminals. This can take place via a power pack, charger or a second battery (e.g. external start).

If using a charger it must have a mode for total discharged batteries or manually starting the charging procedure. Otherwise the battery will not be detected and the charging procedure will not start.

Fig 1: Identifying Battery Housing And Mounting Bracket

Courtesy of BMW OF NORTH AMERICA, INC.

Item	Explanation
1	Battery housing
2	Positive battery terminal
3	Mounting bracket
4	Negative battery terminal
5	LIN bus connection
6	Vent hole

The following graphic shows the general inner views from the front and the rear.

Fig 2: Identifying Cell Module And Battery Electronics Module

Courtesy of BMW OF NORTH AMERICA, INC.

Item	Explanation
1	Cell module
2	Measuring resistor (precision resistor)
3	Battery electronics module
4	Battery isolating switch (relay 2)