Acceptable resting battery voltage for new alternator?

[80stech]

The whole "no warranty on alternator if installed with dead battery" came into play in the 90's when GM came out with the tiny high amperage alternator that would melt if it was ever called upon to put out it's rated amperage. This was mostly the rebuilders covering thier ass for a poor design. Other than that, only a shorted battery could be an excuse but even then, before the poor GM design even a shorted battery usually didn't kill the alternator.

[mtthmpsn]

Thanks for all the responses. I didn’t get a chance to run the gamut of tests or scans outside of resting and idling voltage, but the discussion here worried me enough to go back to auto zone to have them test the battery. Their test confirmed that although charge was at 100%, it was a “bad battery”. Kudos to them for replacing it no questions asked. If nothing else, i have peace of mind about the alternator now. Hopefully this thread will help others going forward. Thanks all!

[StephenVA]

Congrats!

Good choice and good out come.

I appreciate that they told you it was a "100% charged battery" but it was still bad. Most mass marketers use a volt meter and a wave form meter and say it's good. As soon as it is accurately load tested with a carbon pile meter (1/2 total CCA at zero degrees, or up to 250 amps for 3 mins) most will roll over and die right in front of you. The surface charge reading (the Voltage reading you get after charging at 3-4 amps for 24 hrs) is nothing more than a few plates holding a temp charge. When a battery shorts out, like the example mentioned in previous post, the battery will absorb 100% of all energy provided in a jump start. Nothing short of by passing the existing battery (pull off the cables and connect them directly to the outside the car source), will allow the dead car to be started with no challenges. Think of a dead battery as a sponge. Everything gets sucked in.

Sorry for the way too long details. A by product of having worked in the auto test equipment market and run training classes for mass marketers, dealerships, repair shops, techs and hobbyists, then for more years as a factory rep. The lack of training, basic knowledge, and repeatable repair process procedures was a constant battle. Example: 95% of electronic sensors being replaced at a warranty level by one of the big three US dealerships all bench tested OK in the lab. Super high returns. Added training classes to tech techs how to quickly determine faults dropped the warranty claims by 64% in 90 days. scary.....

[andrewwynn]

It's your car me enough to need to register the battery? I don't know if that came about at the E70


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[LVR]

Hi I wonder if I might ask a dumb question....

My 4.8is has been sitting for over 12 months without being driven before I got it. Have noticed that the air compressor came on recently then stopped and the car hasn't righted itself since. Ordered a compressor repair kit but in the meantime thought about the possibility of low battery charge stopping the compressor working?

Then the last 2 days the car is a little reluctant to crank.

I don't have a meter to check the battery but do have a BMW branded CTEK charger that I use on my 4.4 without problem. I went to use the charger but it won't initialize ie it won't change mode. From the limited info I can find online about this it does this when the battery charge is too low. Apparently it needs a 'jump start' to get initialized by bringing the battery up a bit. I have one of those 900mah jump starters that can charge the battery but figured that's just too risky to do without advice....

So to the dumb question... any ideas on how to get the charging to initialize?

And yes, off to buy a meter to check the battery...

Cheers

[wpoll]

Originally Posted by LVR

...

So to the dumb question... any ideas on how to get the charging to initialize?

And yes, off to buy a meter to check the battery...

Cheers

You might need to remove the battery from the car and charge with a 6 or 10amp charger, then get it tested. But watch the voltage, charge current and battery temp while doing this - if the battery is VERY flat it may be rather hard to save it. If the open circuit (no load) voltage is less than 9 or 10volts, it's likely toast.

[wpoll]

Originally Posted by andrewwynn

It's your car me enough to need to register the battery? I don't know if that came about at the E70


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No E53 needs to have the battery registered. This came in on the E70 etc...

[StephenVA]

+1/\

[LVR]

Ok, So I checked the battery charge at rest after 2 days sitting without use and at the battery it is reading 12.05 Volts.

From a Bimmerboard chart I saw posted by Qsilver7 in another thread, this appears to be a 25% state of charge. Is that right?

If that is, then that would explain why the Ctek I have won't initialize?



I'm thinking I need a bigger charger? Or do other tests?

[wpoll]

Originally Posted by LVR

Ok, So I checked the battery charge at rest after 2 days sitting without use and at the battery it is reading 12.05 Volts.

From a Bimmerboard chart I saw posted by Qsilver7 in another thread, this appears to be a 25% state of charge. Is that right?

If that is, then that would explain why the Ctek I have won't initialize?

...

I'm thinking I need a bigger charger? Or do other tests?

I think it would be best to proceed directly to a load test - see if the terminal voltage falls dramatically when a modest load is applied (say 5 amps or so). If the voltage drops really low (9-10v) then the battery is likely a goner... even at 25% charge, a good battery should sustain a few amps for a minute or two without dropping down too low in volts.

You could also perhaps try a bigger charger (if you have access to one) for something like an hour and see if the no-load voltage comes up at all. If it does, then try switching back to the BMW charger and see if it will start charging.