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Old 12-05-2011, 05:23 AM
sunny5280 sunny5280 is offline
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Originally Posted by yikes98 View Post
There are other energy hogs that nobody thinks of. The stuff you can touch and turn on is one type, the other is the stand electronics for the computers to boot everything up, to get O2 heaters, cat heaters, throttle valves, variable valves timing, injectors, HP fuel pumps, starter,etc, etc, etc...Obviously it depends on the engine package but everything has to work right away to keep emissions low right after start because that usually where most of the bad air is made on the cold start and one of the areas where certification is required. You don't make gov. emissions numbers, you don't sell cars. BTW power budgets are going to get even worst as OEMs push for cleaner and cleaner technologies in conjunction with more and more luxo features.
I mentioned the options because they are what set different cars apart wrt electronic consumers. I assume the remaining electronic consumers are common to every E9x model.

As for electronics having to boot I see no reason why these systems would require any lengthy initialization time. If they have to remain in a low power state which consumes enough power to exhaust a battery in a short period of time then they've been designed wrong. I don't hear about this issue with other manufacturers so BMW must be doing something wrong if you can't leave a car sit for a reasonable amount of time. Since I haven't experienced this issue (with leaving the car sitting for an extended length of time) I can only assume BMW has got it right. As I said I left my 2006 330xi sitting in the garage for extended periods of time (often a month, sometimes two) with short trips in between it sitting. The battery held up fine.

Personally it's been my experience when a battery begins to exhibit behavior as described by the OP that's an indication the battery needs to be replaced. Take my 1999 328i for example. It sat in the garage and one day I went to start it and it failed to start. Thinking I had left it sit too long I charged it and took it out for a long drive. Came back the next day and drove it again. Came back after a week and it was dead again. Lather, rinse, repeat. Ended up buying a new battery and that's the battery that was in the car when I sold it in August 2010. It was still going strong.
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