Battery condition
The battery condition cannot be determined based on the battery state of charge alone. All batteries are subject to natural wear due to the natural ageing process. The chemical reactions in the battery, consisting of the charging cycles with battery charging and discharging, mean that deposits form in the battery, preventing the battery from reaching full capacity.
| Item | Explanation |
|---|---|
| 1 | Charge battery. |
| 2 | Discharge battery. |
| 3 | Ageing/deposits |
| 4 | Self-discharging. |
Each total discharge results in a loss of battery capacity: The longer the battery remains completely discharged, the greater the loss of battery capacity. The batteries installed at BMW and MINI can withstand several short total discharges or up to two long total discharges, however, when they are fully recharged with a constant charging voltage of 14.8 V after the total discharge. The diagnosis system determines the battery condition using the following criteria:
- Ageing: The energy flow rate (cumulative discharge) and the voltage dip evaluation from recent engine starts are evaluated as the measured variable.
- Damage due to total discharges or operation at a low state of charge: fault code entry and the time in a state of charge below 20 % are evaluated as the measured variable.
If monitoring of the battery condition identifies an aged or defective battery, a fault entry is registered in the engine control unit. The fault entry can only be deleted once the battery is replaced and the battery replacement was registered.
Notes for Service department
General notes
The battery may only be recharged with a battery charger that has been approved by BMW and that has a constant charging voltage of 14.8V.
If possible, the battery temperature should be between 15 °C and 25 °C during charging. Under these preconditions, the battery is adequately charged when the charge current drops below 2.5 amps.
If the battery is recharged at low temperatures, the charging procedure should not be ended until the charge current drops below 1.5 A.
On vehicles with IBS, recharging the battery directly at the battery terminals could lead to a misinterpretation of the battery condition and even unwanted Check Control messages or fault entries.
If the battery is recharged while it is installed, it must be recharged using the jump start terminal points, whenever jump start terminal points are provided in the engine compartment. Only then can you be sure that charging is correctly recognized by the vehicle electronics on vehicles with an intelligent battery sensor (IBS).
Except for MINI from R55 model: These vehicles do not have any jump start terminal points in the engine compartment. On these vehicles, the positive terminal of the battery charger must be directly connected to the battery. On vehicles with a petrol engine, the negative terminal can be connected to the lifting eye (suspension lug) on the transmission and on vehicles with diesel engines to a flange on the engine bearing block on the engine.
In the case of stored or stationary vehicles the battery must be recharged at regular intervals in order to avoid a total discharge and thus damage. See the following information: Battery recharge interval for booth vehicles.
After replacement of the battery and registration of the battery replacement, or after replacement of the intelligent battery sensor (IBS), the vehicle must be in rest state for at least 3 hours: Only then can the new state of charge be determined by open-circuit voltage measurement.