BMW starting & battery charging system

In our automobiles the battery is the one which provides the electricity to start the engine. Long time ago we could just jump start our car if the battery went weak or dead. All was well after, since the alternator kept all going just fine beyond the jump start. Today that is no longer the case.

Jump starting your modern car may have unexpected and costly consequences, some expensive electronics may become permanently damaged, costing serious downtime and money.

A modern, today’s hight tech automobile starting and charging system is as sophisticated as is the modern automobile itself. You may heard the phrase the “efficient dynamics” (BMW) and you may wonder what it means? Let us help you to understand a small part of it. The current management system as intended by BMW and Mercedes-Benz.

In the case of BMW it’s a combination of electronics working together commanded by the engine computer to optimize the charging and maintaining of the electronics in your BMW. The alternator will be turned on only when it’s required by the combination of battery voltage and the demand by the driver driving habits.

This has been developed to manage the starting capability of the engine and the optimization of the on board electronics at the least amount of drag generated by the alternator, while driven or if the vehicle is stationary. No demand has been registered by the ECU and the battery has been charged full, the alternator will freewheel until the demand goes up or the battery charge has been depleted far enough to have the alternator being turned on again.

 BMW 5 Series ECU BoxBMW 5 Series ECU Box

The engine ECU will also disconnect the alternator at full throttle to be able to exert maximum power from the engine as its demanded by the driver. This is all managed by a microchip embedded in the negative battery cable and reporting in real time to the engine computer (ECU), in the event of low state of charge in battery while stationery the, intelligent battery sensor, (IBS, BMW speak) will shut down all the power to try to preserve engine restart when needed. Clear sign is the clock showing blank information as there is no time registered.

Please note the IBS sensor is an essential part of the vehicle’s electrical system which reporting at all times when data can be recalled by the appropriate diagnostic software for evaluation if required. The data will be available including the amount of trips and the length of trips taken also being logged for future evaluation by the technician as long as the battery has not been disconnected when all the data will be erased in the ECU.

It’s very important NOT TO disconnect the battery even if the battery is depleted, because all the data will be lost if the battery cable has been removed. The battery must be registered in the engine ECU after replacement with the type and the capacity for the ECU to be able to use the right algorithm for the current management (battery charging protocol) which has to be programmed with the BMW software.

We hope this helps to understand the concept of the modern automobile charging and current electrical management system.

Happy motoring from your European auto technicians at Techmax.


To prevent breakdown and keep you on the road safely, we use Midtronincs GR8-1200 Electrical System Tester – Analyzer to check, test your automobile electrical system. Read more…