Tech Tip – Things You Don’t Want To Find In The Back Of Your BMW (9 photos)
1) Incorrect battery type and size.

2) Not battery venting – explosion hazard.

During the diagnostic for a electrical fault on this BMW, we uncovered some problems why the car was towed in. First, the incorrect size and type of battery had been installed, “Duralast” is not a factory BMW battery, and these cars are very touchy on correct voltage and battery type.

Second, and perhaps more concerning, was that the battery venting pipe was never installed. A byproduct of battery charging is hydrogen gas, which is highly explosive – think Hindenburg. So a trunk or interior mounted battery must be of the non-venting type, or have a proper vent hose installed, otherwise hydrogen gas can build up inside the compartment, and potentially cause an explosion. Reference –

In addition, the aftermarket battery only lasted about 2 years, and resulted in a problem requiring the vehicle be towed to our facility.
The electrical system in late-model Minis and BMWs is quite sophisticated, in that it tailors charging as closely as possible to both the type and age of the battery. The Engine Management computer also controls the alternator output. When replacing a battery, this computer needs to be informed 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 advised 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.

We have diagnosed some BMWs with failing batteries, some installed less than a year, simply due to failing to have the battery registered! The charging system often shortens the life of an unregistered battery by charging it too aggressively, especially when it is cold, and sometimes damaging other control units. At times, we have replaced an alternator that failed prematurely because battery registration was not performed when the vehicle’s battery was replaced.

Most late model cars are very dependent on a stable and properly operating electrical system, generic battery replacements, jump starting, or even weak batteries can wreak all kinds of havoc with your auto.

Questions, not sure, or want a second opinion?
Just call us, (207) 882-9969, we’re here to help!