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      07-07-2017, 09:53 AM   #26
gjm120
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Drives: 2013 128i, 2021 230i
Join Date: Jan 2016
Location: East Texas

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Quote:
Originally Posted by JimD View Post
Nice DIY. My wife just had her's done at the dealer for a little less than $400. I won't go that route when my 2009 goes. She really likes to go to the dealer and her battery also failed catastrophically. We had to jump from both ends to get it to start - it would take no charge at all.

I looked at just putting a battery in it and dealing with the coding later, the path I intend to take with mine, but the lack of amp hour ratings on US batteries slowed me down. Her's was rated 80 am hours but only 140 reserve capacity. I found a conversion on line that said to multiply reserve by .4167. Doesn't work for that battery. It's CCA were only 650. Pretty small battery.

What do you guys do when you don't really know the amp hours. Take a reasonable guess?

This formula gets pretty close: RC *(0.449) + 12.4
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