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      03-11-2013, 05:00 AM   #1
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Battery Replacement and understanding the reason for coding?

Hello guys,

I think i have tracked my "high discharge error" and battery low warning troubles down to a dead battery. I can't seem to get the battery to hold any sort of a charge so i guess its time to be replaced....

My car is a 2010 and has done 44K and it still looks like the original battery from new in there. When doing a search it seems that some M3 develop battery problems from as little as 18-20K. Mine is double that!

I have been quoted 320 for a BMW main-dealer to OEM replace it, however having a full work-shop and garage setup i'm reluctant to pay that. BMW said it won't take any longer than an hour! What a price....

My main problem isn't sourcing a battery its the coding that could need to be done after, however looking at the car the only connectors to the battery are the + & - so this leads me to think:

IF I REPLACE THE BATTERY WITH IDENTICAL SPEC'ED AS WHAT WAS IN THERE WILL MY CAR NEED TO BE RE-CODED? If so how does the car know the battery has changed? What will happen if i replace the batter but do not get it coded? Error messages? The low battery illuminated the Engine light on my dash which sucked as i only had the car for 2 days before this happened making me think all sorts of stuff could be wrong with it..

This is the battery that was in my car:

Also, the OG battery is EXTREMELY HEAVY. Anyone know anywhere in the UK that sales lightweight batteries? Wouldn't mind loosing a bit of weight, i can see that Euro Auto Source in the USA does them but they won't ship one overseas for me

Thanks guys
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      03-11-2013, 06:46 AM   #2
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I replaced my battery after 5 years and i didn't code anything.

Speaking of a lighter battery:

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      03-11-2013, 10:53 AM   #3
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I have always heard without coding the battery will wear out more quickly as the computer adjusts the draw from the alternator based on battery strength or health but have no idea how it monitors this
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      03-11-2013, 10:55 AM   #4
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I replaced my battery after 5 years and i didn't code anything.

Speaking of a lighter battery:
Thanks mate! Much appreciated.

Just took my battery to a very highly recommended local battery supplier and they ran a few tests on it and it came back as "good" by them. Still holding 80% of the charge and they don't seem to think its the battery fault for my loss of power....

So, where do i go now....I got a car that will within 24 hours drain a completely charged battery to the point where it won't even crank the engine over. Just flicking electrical instruments. Making it impossible for me to drive anywhere or leave it as i'm scared that i'll come out and not be able to start the thing. Plus you look like a total twat in an M3 that won't start...

Can't believe it as i've had the car less than a week and driven it about 3 times. I'm not impressed in the slightest.

Hopefully i don't have to sale a car just to fund the repairs on this one!
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      03-11-2013, 10:57 AM   #5
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Originally Posted by tom @ eas View Post
I've been wanting to post a tech article about this subject for some time, might as well start now:

Absorbent Glass Matt Battery (AGM)

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).

Service Instructions for AGM Batteries
When handling AGM batteries, certain special factors must be taken into consideration with regard to battery renewal and installation location:

Do not charge AGM batteries with 14.8 volts or use use rapid charging programs
When charging batteries in the "stand alone" mode, the maximum charge voltage of 14.8 volts must not be exceeded. Even briefly charging an AGM battery with a charge voltage of more than 14.8 volts (voltages usually used in rapid charge programs) will damage the battery

Do not install AGM batteries in the engine compartment
Because of large temperature variations, AGM batteries must not be installed in the engine compartment. This would result in a significant reduction in the service life of the battery

Do not open AGM batteries
By no account should AGM batteries ever be opened, as oxygen from the atmosphere would cause the battery to lose its chemical balance and cause it to fail.

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.

Note that replacement batteries resulting from a customer's driving profile cannot be claimed under warranty.

Battery Replacement Registration

This Service Function informs the PM 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
Hope this helps.
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