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      05-16-2009, 05:11 PM   #61

Drives: M3 coupe
Join Date: Apr 2009
Location: Louisiana

iTrader: (0)

Originally Posted by 808MGuy View Post
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.
Actually a "dead" battery will usually be in the 10-11 volt range. It could be even lower if a sustained load was applied after the engine was shut off.

Once a battery has been totally discharged once (run all the way down) it typically never recovers 100% of it's capacity. Some manufacturers will tell you this upfront, while others will not.

FYI: It seems that some of you are confused on how these batteries work. They are not "charged" by a battery charger at the factory before they are shipped out to dealers or directly to customers.

The battery shell (plastic casing + LEAD lined glass mat plates) is filled with ACID which starts a chemical chain-reaction that 'activates' the battery right before they ship out to prospective customers. It's ready to go when the box it up for shipping. No power is lost or gained until it's installed up to about one year. If you are reading a low voltage on these Braille batteries, either that's how they come from the factory, or the acid was not filled to the proper level.

Those are the only 2 practical explanations, outside of some serious internal parts defect they have not identified to date.

If needed, these batteries CAN sit on a shelf for about a year without suffering any significant loss in voltage.

These racing batteries have a very low discharge rate if NO LOAD is present.