In all this, the battery must not only be able to supply energy for these engine restarts, but must also power the users when the engine is switched off.

In this sense we can say that the battery is now the heart of every car.
The battery status is monitored via a control sensor, in the FCA world called IBS (Intelligent Battery Sensor see detail ) system that can be adopted on European standard batteries.
So if the system start & stop does not work, the reason is to be found in the interaction between these two important components.

If the main task of the battery is to start the engine and it does not has the required minimum state of charge, the control unit (IBS) deactivates the function start & stop in order to facilitate engine start-up in the first place.

This may occur in the following cases:

• the mounted battery is not compatible and can only provide a minimum number of charge/discharge cycles.
• The outside temperature is too high or too low. For example: s and the battery needs too much energy to power the fan, the start & stop will be deactivated. When, and if, this happens, however, depends on the comfort settings set by the vehicle manufacturer. In this sense p t could happen, for example, that the  start & stop continue to operate and instead turn off the air conditioning.
• The engine temperature is too high or too low.

Battery-independent factors

However, there are also factors independent of the battery that interrupt the function start & stop :

• seat belts are not fastened
• the door or engine bonnet is not closed properly
• parking assistant is active
• the vehicle is travelling on a steeply sloping road