battery reserve capacity rating

This sounds like a terrible to ask but, what is the minimum voltage through the car to keep it running after the alternator has stopped providing a charge. my battery is 650 cca and turns into 11.8 thru the obc. what's my reserve capacity at 20*F, how can i calculate from the difference in normal calculation from 80*F at a 25A discharge. w/o any external accessories besides bi-xenons, cluster full dim, will it hold over 10.5 volts for 30 miles / 30 minutes of driving?

OKAY!

Easier question?

Can I drive for a while and maintain driveability (i know i'll lose dsc/abs eventually) with battery light already on?

It will quit starting, at 10.8V
I had to drive my car on a bad alternator to pick up my new alternator.
I began with a full charge 12.8V
It was driveable as low as 11.2V
By the time I got home to replace the alternator, I turned the car off, went back to menu 7 in OBC and saw that it had fallen to 10.8, and wouldn't start.
It was day light, and ac, radio were off.

BTW...you will have ABS DSC, they usually die just seconds before the car dies, in my experience.


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There is some correlation between voltage and state of charge, but it's not definite; there is no formula, and it's dependent upon the age, condition, and quality of the battery (plus other factors). RC is RC, regardless of temperature, but you can't use 100% of it on a brand new battery, and you're not at 100% state of charge anyway.

You can drive on battery voltage with a dead alternator, but the car will shut down noncritical systems like ABS/DSC/radio/etc as mentioned. You will generally get very little warning before it dies, in my experience. 30 minutes is very doubtful without a full charge to begin with. You'll also hurt your battery, if not kill it.

I drove my car without alt on 12/23/12...it was a 1 year old battery...alt was original at 244K miles. I drove at night, without heat, for 30 miles...and was amazed.

Near the end, my voltage had dropped to around 8 or lower. The car stalled at one point near the end as I was going up a hill. Put it in reverse, 'push' started it, kept the revs up and made it the last mile.

I was amazed.

Anyway, put the battery on a charger, replaced alt, I'm all good now...battery is fine afaik.

HTH (But, don't drive it if you don't need to...and don't stop the car...and turn off all non-critical electric things)

Charge the battery first. If you drive in daylight (no lights, and ideally, no DRLs....even at 1/2 power, the std halogens eat more juice than the HIDs), no defroster (front or rear) or AC, don't move the seats, etc. you shouldn't have a problem with 30 mins of driving. Having a manual is a big plus: you can keep revs low (and thus spark need and fuel need), plus, as dmax mentioned, push starting is an option.

If there are only 2 pedals on the floor, consider not shutting off the car when picking up the alternator. Or carry jumper cables and let the other battery charge yours a bit before starting.

GL