Bimmerfest BMW banner

61 - 80 of 85 Posts

·
Anti-Hack
Joined
·
4,835 Posts
I let the battery charge fully overnight (12.49V) took the negative cable off in the morning (8am). Just got home (5pm), attached the negative cable back on and the volts dropped to 12.32V. Car started without hesitation.

This is on the old battery? That is a large voltage drop unhooked for sure, much worse than my 18 yr old E21 battery.

Hopefully the new battery solves the issue, otherwise there’s be some more diagnostics to do. I’m personally skeptical of another issue but I’m always skeptical.

Did you look for a 25% coupon for AA?

IME one of their flooded batteries is going on almost the same life as 2 BMW batteries in my car. FWIW.


Sent from space
 

·
Registered
Joined
·
529 Posts
Discussion Starter #62
This is on the old battery? That is a large voltage drop unhooked for sure, much worse than my 18 yr old E21 battery.

Hopefully the new battery solves the issue, otherwise there’s be some more diagnostics to do. I’m personally skeptical of another issue but I’m always skeptical.

Did you look for a 25% coupon for AA?

IME one of their flooded batteries is going on almost the same life as 2 BMW batteries in my car. FWIW.


Sent from space
Yeah it's on the old battery. I called advance auto and they said that much of a drop is fine. I called a BMW shop, they told me that much of a drop is not normal. Idek who to belive :cry:
 

·
Anti-Hack
Joined
·
4,835 Posts
Yeah it's on the old battery. I called advance auto and they said that much of a drop is fine. I called a BMW shop, they told me that much of a drop is not normal. Idek who to belive :cry:

That may be but and does correlate with their load tests; I don’t see that drop on mine.

Short story: the 8 yr old battery on my Olds failed after sitting most of the year (no trickle charge and only 6k miles in that time), and the new one died in 2 months. Load test on one set of terminals passed but on the other set failed (battery had both top and side terminals). Battery had an internal fault.

You need to let it go longer than a work day to see if the discharge rate changes. Ty letting it go a week if you can. Is the rate variable or linear? If you’re looking to save money that’s what I’d do.


Sent from space
 

·
Registered
Joined
·
529 Posts
Discussion Starter #64
That may be but and does correlate with their load tests; I don’t see that drop on mine.

Short story: the 8 yr old battery on my Olds failed after sitting most of the year (no trickle charge and only 6k miles in that time), and the new one died in 2 months. Load test on one set of terminals passed but on the other set failed (battery had both top and side terminals). Battery had an internal fault.

You need to let it go longer than a work day to see if the discharge rate changes. Ty letting it go a week if you can. Is the rate variable or linear? If you’re looking to save money that’s what I’d do.


Sent from space
So, pull the negative cable off for a week and see how low it drains? Noting the voltage before taking the cable off and after.
 

·
Anti-Hack
Joined
·
4,835 Posts
So, pull the negative cable off for a week and see how low it drains? Noting the voltage before taking the cable off and after.

That’s what I’d do before buying a new battery, if for no other reason than to know. If the battery reads 12.30 or 11.9 can tell you a lot. You may very well need the battery... but again cheap and skeptical.


Sent from space
 

·
Registered
Joined
·
529 Posts
Discussion Starter #66 (Edited)
That's what I'd do before buying a new battery, if for no other reason than to know. If the battery reads 12.30 or 11.9 can tell you a lot. You may very well need the battery... but again cheap and skeptical.


Sent from space
Lowest it went was 12.37V (before pulling negative cable off) to 12.2V(after putting cable back on) within a few hours (6-8 hours unplugged) Every time I put the charger back on the car, the charger shows that the battery is only 50% charged (after putting negative cable on). Yet, it was "100%" charged like 12 hours ago.
 

·
Registered
Joined
·
529 Posts
Discussion Starter #67
So the battery is fully charged and is reading 12.42V. I have taken the negative cable off and will let the car sit like this for a week. Unless I need to cut the grass on Friday or Saturday.
 

·
Registered
E93 335i, somewhat mod <> Fog City, CA
Joined
·
2,267 Posts
So the battery is fully charged and is reading 12.42V. I have taken the negative cable off and will let the car sit like this for a week. Unless I need to cut the grass on Friday or Saturday.

Lead/acid batteries have an internal resistance and will go dead with time, but 1 week's nowhere near enough for a healthy unit. Good show.

Did you run a parasitic draw test?
 

·
Registered
Joined
·
529 Posts
Discussion Starter #69
Lead/acid batteries have an internal resistance and will go dead with time, but 1 week's nowhere near enough for a healthy unit. Good show.

Did you run a parasitic draw test?
Did you run a parasitic draw test?


Not yet, if the Volts go lower then 12V I think I'm gonna go ahead and replace the battery.
 

·
Registered
Joined
·
529 Posts
Discussion Starter #77 (Edited)
Whoop, the amps high because I didn't let the car "go to sleep". Now that is sleep, that draw amps are 1.46. NOW it's time to either pull fuses or check them with the multimeter
 

·
Registered
Joined
·
529 Posts
Discussion Starter #78 (Edited)
I let the car fully got to sleep. All the lights turned off (trunk light, gear shift level light etc) and the amps are down to 0.01. So, I don't think there's a shortage. Maybe a bad battery at this point or the car just sits for too long
 

·
Registered
Joined
·
2,000 Posts
I'm confused. Are you driving the car at all? So, you charged the battery, let it sit, and battery drained, or you charged battery, drove, let it sit and battery drained? The batteries have been good and the alternator tested good, too. So, if the battery isn't dying just sitting their without driving, i'm not sure all the talk about ground cable and parasitic drain. If you are driving in between and the battery isn't fully charging after driving, but the alternator is good, then it is something else that is causing it. I know on my e90 and other folks' e90s, a bad harmonic balancer was the root cause of the battery not fully charging and dying.
 

·
Registered
Joined
·
529 Posts
Discussion Starter #80
I'm confused. Are you driving the car at all? So, you charged the battery, let it sit, and battery drained, or you charged battery, drove, let it sit and battery drained? The batteries have been good and the alternator tested good, too. So, if the battery isn't dying just sitting their without driving, i'm not sure all the talk about ground cable and parasitic drain. If you are driving in between and the battery isn't fully charging after driving, but the alternator is good, then it is something else that is causing it. I know on my e90 and other folks' e90s, a bad harmonic balancer was the root cause of the battery not fully charging and dying.
A few weeks ago, I went to start my car and the car didn't start. So, I pulled the battery out and took it to advance auto to have them test it and see if the battery is good or bad. They kept the battery overnight and turns out the battery was fine. Now, last week the battery died, once again. So I kept it on a trickle charger to let it charge fully. My assumption is, the battery died because the car sits for too long. There is no parasitic draw.
 
61 - 80 of 85 Posts
Top