You're right about the recoding voltage, BMW specifies a minimum in all their related SIB's.
As far as the old wives tale thing, I believe what you heard, I just don't know if it's completely accurate. All the chargers seem to have their own proprietary formula for optimal charging. Unlike what you heard it's my understanding that AGM batteries apparently prefer higher voltate charge so an option like the Battery Tender Plus which BMW itself sells, and outputs at 12 volts/1.25A, really isn't such a great choice compared to a CTEK charger that outputs 14.7 volts/3.3A in its specific setting for AGM batteries. And hogwash or not, it's interesting to note that the Porsche rebranded CTEK charger does not have a AGM setting since Porsche didn't use AGM batteries and so they didn't want someone to charge at 14.7 volts (I spoke to CTEK about this). Now will both get the job done? Probably. But unless someone did a head-to-head test over the lifespan of the batteries I think it would be impossible to know for sure if one is better than the other. In BMW's SIB on charging they specifically call for the Deutronic charger to be set at 14.8 volts constant voltage while they don't specify the output current. So that's interesting to note as well.
Quote:
Originally Posted by E55AMG2
I'll invite you along with me to the PRI (performance race industry) show next year. I spoke with the mfgs of all of the above mentioned batteries. Braille, the manufacturer of the battery I linked they told me it's more or less marketing hogwash. All of their batteries (AGM or wet) are designed to be charged anywhere from 12-14.1V (ie the output of an alternator). What's most important is amperage. They told me their car batteries work best when tended at 2A at a minimum of 12V. So long as the charger makes at least 12V and 2A, it wont make one lick of difference. I've owned Optimas and Odysseys as well....all worked perfectly fine with my Die Hard (rebadged schumacher) battery charger at 2A. So unless my charger is magical, Im pretty sure it's just an old wives tale.
The only thing that's voltage critical is when you are trying to code modules or reflash firmware. I'd want a minimum of 12.5V for doing any of that.
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06-16-2011, 12:34 PM
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