[cdm244@gmail.com]

My take on E90 battery anomalies:

On my 2011 (a 6mt - n51) even with a new & registered battery I was losing starting capacity after only a few days of inactivity. Turns out it was battery sulfating due to short trips - in fact in the winter I was just starting up and backing out of the garage every few weeks and letting it warn up to operating temperatures (210 or so) for 20 minutes and pulling back into the garage. This was not allowing a full charge and was allowing sulfating to occur. Now at times of low usage I take a nice 30 mile trip every few weeks down the interstate (in 5th gear to keep the rpms up) to make sure that I'm at a high state of charge when I return. A good check with volt meter:

> 24 hours after use you should see a good 12.6 or so
> a day latter maybe a loss of .01, so maybe 12.59
> each day afterward look for another .01 decline

So, after 2 weeks your 12.6 should be around 12.45 - still healthy though I can see why these cars - as known battery hogs - can't be left at an airport for much over a month as state of charge drops 12% for every .1 v in loss. State of charge below 50% will probably result in a no start. Even with the normal parasitic drain of 10 - 20 ma (1/100 to 1/50 an amp) a 90 amp hour battery is dead quicker than we would expect.

[EB89]

Get a charger, problem solved

[Three_thirty_I]

^^^ Invest in a Ctek or other good smart charger - this will help hugely!