[Zyal8r]

My battery charger included some great info about batteries. The voltage starting with a dead battery is 11.4vdc and goes to 12.9vdc fully charged so there is only 1.5v difference between a dead battery and a good one. A 50% charge would be about half way in between for example. An older battery won't fully charge because it is sulphated (?). And it won't tolerate a current load very long. Most auto supply stores will do a load test for free.
SEARS REGISTERS BMW Batteries for $79.00. They showed me the program on their monitor. They also charge for the installation. The batteries are highly rated and you save over $100 versus the dealer. You can save more by buying on line and installing it yourself and having them register it.
If you don't drive your garage queen much, running a good charger will greatly increase the life to more than 6 years by reducing the sulphating.
I find that a new battery will have between 12.4 and 12.9 vdc I guess depending on amount of night driving and top actuations. With engine running about 13.2 or more but this probably is more of a test of the system.
AGM seems to be the way to go but older oems are lead acid.
On my car the first sign of trouble was that the clock would not hold its setting and a ! symbol came on. Resetting the time only worked for a day or less. I have heard of other wierd clues.
Some of the newer solid state chargers claim to be able to revive a sulphated battery with a special long slow charge cycle.