06-02-2020, 03:02 PM | #1 |
Solving problems
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,279
|
Battery dead?
Miata battery seemed dead out of the blue yesterday. Jumped it with the LR4 with no problem. Let it idle for a few minutes (we were going somewhere) and shut it off. Today, once again dead.
New jump, this time with a bit more effort and got it going. Drove for an errand about 25 minutes of very spirited back roads and high speed driving. Got there, went in for 5 minutes and again car would not start when I got back. Had to get a jump. Same return drive home. Voltage after shutting it off when I got home = 12.05V Voltage after 1 hour = 11.85V Voltage after 2 hours = 11.80V The battery had a couple of episodes of being drained early on. It (Duralast Gold) was bought a couple of years ago because I thought the previous battery was the issue, but it turned out to be loose connections. That's not the case now. Everything is tight. |
06-02-2020, 03:06 PM | #2 |
Alphanumeric
Join Date: Aug 2005
Carmudgeonly Ride: 981S, 340i
Posts: 9,587
|
I guess it has a warranty?
|
06-02-2020, 03:08 PM | #3 |
Old Fart
Join Date: Oct 2005
Carmudgeonly Ride: T4R,GTI
Location: San Diego
Posts: 8,576
|
just bump start it
|
06-02-2020, 03:09 PM | #4 |
Solving problems
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,279
|
|
06-02-2020, 03:20 PM | #5 |
Solving problems
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,279
|
|
06-02-2020, 03:41 PM | #6 |
Chief title editor
Join Date: Oct 2003
Posts: 26,599
|
Alternator?
__________________
OH NOES!!!!!1 MY CAR HAS T3H UND3R5T33R5555!!!!!!1oneone!!!!11 Team WTF?! What are you gonna do? |
06-02-2020, 03:50 PM | #7 |
Solving problems
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,279
|
That's what I am wondering. The car worked flawlessly when it was running, something that didn't happen the only time I've had an alternator go bad. The battery didn't seem to charge well, but that could be the battery. I'd think that right after that long drive the battery should be at over 12.0V.
|
06-02-2020, 07:34 PM | #8 |
older fart than ZBB
Join Date: Oct 2003
Location: On the road again
Posts: 8,911
|
After jump starting, alternator output should be 14-14.2 volts. Headlights should be fine running from the alternator, not the battery.
Loose belt can also effect alternator output
__________________
2017 GMC Sierra 1500 SLE 2020 Fusion Titanium |
06-02-2020, 07:56 PM | #9 |
Solving problems
Join Date: Oct 2003
Carmudgeonly Ride: M5 / 718 GTS / Cooper S / GTI / LR4
Location: Metro Boston
Posts: 25,279
|
I just replaced the belt preemptively a couple of weeks ago. Ironically, I had to pull the battery and it's cradle to get to the belt tensioner. All was fine for a coupe of weeks and a few drives.
|
06-02-2020, 08:12 PM | #10 |
Relic
Join Date: Oct 2003
Location: Bethesda, MD
Posts: 12,475
|
Start by testing alternator output voltage. If it's above 13.5 or so, it's probably fine.
The battery will not stay over 12v for long once the alternator is off it. If the alternator is good, disconnect the battery and see if it discharges overnight while not hooked up to anything. Or, as an alternative, take it to an auto parts store and ask them to test it. The gigantic, expensive battery conditioners that they have can rehabilitate a battery that home chargers can't.
__________________
2011 M3 2006 Sierra 2500HD 4WD LBZ/Allison 2004 X5 3.0i 6MT 1995 M3 S50B32 1990 325is 1989 M3 S54B32 Hers: 1989 325iX 1996 911 Turbo |
Bookmarks |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Dead battery on the e46 m3 | equ | Technical Superiority | 19 | 01-24-2016 06:45 PM |
P-car battery dead, what a PITA | FC | Car Talk | 10 | 01-16-2013 12:14 PM |
Dead battery in the E46 M3 | TD | Technical Superiority | 25 | 01-23-2012 02:40 PM |
Now my battery is dead in the M3 | TD | Car Talk | 119 | 01-26-2004 10:34 AM |