View Single Post
      05-15-2009, 08:39 PM   #53
Major General
lucid's Avatar

Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

iTrader: (0)

Originally Posted by swamp2 View Post
Let's do some math. Lets say HP was right about 50 mA to keep CA and other idle processing going. Heck, let's double that just to be conservative. 100 mA x 72 hours (3 days) ~ 7 Ah. What does 7 Ah mean to a 30 Ah battery. Well at such a low current draw over a longer period of time (the 31 Ah spec is at 20 hours) the battery will have even a greater Ah rating probably 25% higher meaning effectively ~39 Ah.
Yeah, I was trying out a similar calculation. Things just don't add up. If the Braille battery indeed has the advertised specs, it should not have problems because of CA over 2-3 days.

I also agree that reducing the OEM reserve capacity of the battery does not explain what we are observing here. That should only be a factor if the car sits around for too long or one demands current with the alternator off. Other than that, the alternator should just charge the damn thing like it charges the OEM battery. UNLESS there is something wrong with the Braille battery and it doesn't like the way the M3's system tries to charge it.

I'll swap mine in soon and see what happens...