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Replacing BMW batteries....yes it is ridiculous

After the posts on Torque Affair's article, I thought I'd shed some light on this subject.

This article was written in 2010, it goes without saying all "F-chassis" cars in BMWs current lineup also have the same battery technology. So pretty much every new model since the Bangle-butt E65 7-series.

The electrical system in late-model BMWs is so sophisticated that it tailors charging as closely as possible to both the type and age of the battery. There's a computer that controls the alternator. When you replace a battery, this computer really needs to know if you've replaced the battery or updated the vehicle from a conventional Lead Acid battery to an Absorbent Glass Mat (AGM) type; it charges the AGM differently than a traditional battery.


This process of updating the alternator-control computer is called Battery Registration. Ignoring the registration process after replacing a battery won't necessarily trigger a Diagnostic Trouble Code or Malfunction Indicator Lamp ('Check Engine' or 'Service Engine Soon' light). However, be warned that skipping the battery registration process can dramatically shorten the life of a battery in these vehicles and- worse yet- damage components within the entire electrical system.

Models that require battery registration:

2002 and newer 7-series E65/66 chassis

2003 and newer 6-series E63/54 chassis

2004 and newer 5-series E60/61 chassis

2006 and newer 3-series E90 E91 E92 AND E93 CHASSIS

2007 and newer X5 series E70 chassis

2008 and newer X6 series E71 chassis

This Service Function informs the vehicle that the battery has been replaced. It completes the following operations:

- Battery capacity is set to 80

- Current Odometer reading are stored. The odometer readings at which the last seven battery replacements took place

can be read off from the Diagnosis Requests of Control Unit Functions

- Stored battery statistics (current, voltage, battery charge level) are deleted

- Stored temperature statistics are deleted

Absorbent Glass Matt Battery or AGM

At the time this was written (6/2010) most European manufacturers use black case batteries to denote an AGM battery and white clear plastic battery cases denote Lead-Acid. U.S. made replacement batteries do not follow this protocol and case color is notan indicator of battery type.


In contrast to conventional lead-calcium batteries, the sulfuric acid in an AGM battery is not held freely in the battery housing. The sulfuric acid is instead entirely bound into the mats of the glass-fiber fleece. For this reason, no acid can escape if the battery housing is damaged. In addition, the AGM battery is a sealed, airtight unit. This is possible because the gasses are converted back into water by the permeability of the separators.


AGM batteries differ from conventional lead-calcium batteries in the following points:

- Larger plates which allow a power density some 25 greater

- Glass-fiber-fleece separators which enable a cycle consistency up to 3x greater improving cold-starting ability, current consumption and service life


- Airtight housing with pressure relief valve

- Inspection plugs sealed and cannot be opened

- Acid bound in glass-fiber fleece

How AGM Batteries Work

AGM batteries differ from conventional lead-calcium batteries in their environmental compatibility and their retention of gases during charging. When a vehicle battery is charged, the electrolysis process emits the gases oxygen and hydrogen. In a conventional lead-calcium battery, these two gases are released into the atmosphere. In an AGM battery, the two gases are converted back into water: The oxygen created at the positive electrode during charging moves through the permeable glass-fiber fleece to the negative electrode, where it reacts with the hydrogen ions that are brought in with the electrolyte, to create water (oxygen cycle). In this manner, the gases, and thus the electrolyte, is not lost. Only when the gas production is excessive, that is when too much pressure is generated (20 to 200 mbar), does the pressure-relief valve open, thereby allowing gas to escape while also preventing entry of atmospheric oxygen. Because the pressure in the battery is regulated by a valve, the AGM battery is also known as the VRLA battery (valve regulated lead acid).


Battery Replacement

An AGM battery, when installed as original equipment, must always be replaced with an AGM battery. In special cases, where a customer's driving profile (e.g. short distance driving), results in a discharged battery, the AGM battery is a recommended replacement.


Don't fret though, there are budget versions of the battery so you don't have to give all your money to the dealership. Duralast (Platinum H6-AGM) makes an AGM battery that is usually half the cost on the OEM BMW part.

Can you do it yourself?

There are many OBD-II programming tools on the market and a few have the capability to register batteries to the new cars. These programs are usually expensive although more options are coming to the market every day to make this problem easier to deal with.


Borrowed from: http://www.evansautocare.com/bmw-battery-re…

And: http://www.munichmotorsport.com/wordpress/?pag…

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