Startability limit

The APM calculates a lower and an upper startability limit for the battery:

• The lower startability limit corresponds to the minimum charge state of the battery so that the vehicle can still be started.
• To counteract discharge down to the bottom startability limit, a certain charge volume is kept as a reserve. To achieve this, the upper startability limit is calculated. This value is used e.g. as the limit value for the requests for deactivation of terminal 30B when auxiliary consumers are active.

The startability limit is calculated by evaluating the following measured variables:

• Average ambient temperature with vehicle parked.
• Ambient temperature of the last journey.
• Current state of charge.
• Voltage dip of the last engine start (trend for ageing of the battery).

The startability limit is therefore dependent on the ambient temperature: The colder the ambient temperature, the more energy required for the engine start. Therefore the startability limit is higher for cold ambient temperatures:

• Startability limit is approx. 30% state of charge at 15 °C.
• Startability limit is approx. 50% state of charge at -15 °C.