Originally Posted by swamp2
Agreeing with lucid here. You (HP) are not only providing incorrect information but you are throwing around a bunch of totally unverified numbers.
An alternator in any car absolutely charges the battery and it does so fairly quickly. Ever have a completely dead battery, get a jump, drive around for 30 minutes and have a totally fine battery? I have. No not in my current car but I'd be floored if it wouldn't work in it.
I also fail to believe that will all power consumers on that the battery will not charge. What kind of nonsensical design would that be? Give the huge teams of BMW electrical engineers some credit. Also, how much variation is there in consumption? The only variables are stereo (and stereo volume - that would be a big one) and interior lights. Everything else will be running normally and running always. Of course some consumers will consume in an rpm dependent fashion.
Our points stand: If the OEM battery can support CA for weeks, then the Braille, operating as per specs can certainly handle a CA for for days. There is plenty of empirical evidence just among the few of us posting here that Braille DOES have one or more problems.
I'm not sure how many times I have to repeat it: The reduced Ah specs for a battery such as the Braille should only really be a factor in cold weather or for long periods of using lights or stereo with the engine not running. Or of course the combination of these.
The alternator should charge the battery but if its totally dead (12.3V is pretty close to that) it will take much longer than a 30 min drive to charge it. Being an AGM battery, the Braille battery should be able to come back from pretty much dead. I mistakenly said it wouldn't before because I thought it was lead acid. While the car is running, the battery is being charged by the alternator and the battery voltage should match the charging voltage of the alternator which is typically somewhere around 14V. What is the voltage reading with the engine on? If it is below 12.5 or so, that means the battery is supplying some of the current and its not being charged.
Has anyone tried using a battery tender or something similar to try and keep the voltage up during long periods (more than a few days) of not driving? Does this help? I still think such a large reduction in capacity has to have its effect on the system but without knowing the actual idle current draw of the system, it's really hard to say for sure.