SUDDEN DEATH (of battery)

JHZR2

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Batteries usually go bad when temperature starting to get colder or hotter.
The extremes are a cause, but not the physical reason. Cold slows chemical reactions so in a capacity limited and high impedance battery, the voltage tanks. Heat increases regrading side reactions which damage the cells and grow impedance. Both result in the same. I’m not convinced that was the issue here. Right now temperatures are pretty mild everywhere.

6-7 year old battery owes you nothing. Keep the NOCO in the car and see how much longer it lasts while searching battery deals. It may last another 6 months and maybe it just got stressed from the constant driving. I'd go for another OEM Subaru battery and dealers often have coupons for under $100.


I think you’re on to something with the constant driving. The plates in batteries shed material as the battery is cycled. I think that long term constant driving results in a very heavy electrode, lots of movement, and thus the ability to shed material. When that material is found in the bottom of the battery case, it can facilitate a path that is an internal short, which then draws down the battery.
 
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It’s from a 2015 Legacy (OEM I think) that I’ve owned and maintained the past four years I’ve owned the car. Never drained. smart-charged every week or so. Can’t be much better maintained than that…

I have a desktop PSU I use to equalize every so often (very infrequently)


6 years on a regular starter battery is quite good especially if it's in the engine compartment.

You did good with it.
 

JHZR2

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That was my thought. I was sure I’d be contacting USAA roadside assistance when I saw the low voltage.

Can battery cells unshort themselves?
I guess it’s possible if it’s loose shed plate material, and there’s enough empty space at the bottom of the battery to distribute.
 

gathermewool

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I guess it’s possible if it’s loose shed plate material, and there’s enough empty space at the bottom of the battery to distribute.

I guess maybe jumping the battery could have broken the soft short and redistributed the lead sediment.

It seems possible but not very likely after thinking about it a little longer, though. If it were to short due to lead sediment I would think that it should not have started when I went to move the car 100’ over to a spot closer to the taco truck we chose. It’s weird that it would start then but not five or so minutes later.

Wouldn‘t the lead sediment need some sort of mechanical motivation to redistribute or would the high draw from the battery pack/starter be enough to move the sediment around?

As an update, I’ve been driving around all week without issue. The voltage continues to read 14VDC+ after starting and while driving relatively short trips, which is all I’ve done since getting back from FL. I’m still going to replace the battery due to the risk to the alternator should it short again. I’m not concerned with getting stranded, since I have the booster pack, which I’ll keep fully charged and in the trunk at all times.

Final thought: I forgot to mention one detail from the No-start instance. When I tried to jump it the first two times (with the NOCO battery pack jumper) nothing happened, not even a click. All loads were off. For the third time I took the key to full off, waited 30 more seconds then went straight to start, which resulted in an immediate and robust crank and start of the engine
 
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Something is definitely broken inside, it can even happen to a new battery. At least you didn’t get stranded. My motto is when in doubt, buy a (quality) new one! Worth every cent.
 

gathermewool

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Just bought a group 25 (OE size) for $80 from Costco. All of the other larger sizes that I saw were close to $100.

I had to sift through to find one that showed a relatively high state of health. One was 12.8V but only 66%. The one I chose was only 12.6V but 87%. I was honestly expecting higher numbers, but the warranty gives me some peace of mind.

I‘ll update this thread with the final numbers are smart charging.
 
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Just bought a group 25 (OE size) for $80 from Costco. All of the other larger sizes that I saw were close to $100.

I had to sift through to find one that showed a relatively high state of health. One was 12.8V but only 66%. The one I chose was only 12.6V but 87%. I was honestly expecting higher numbers, but the warranty gives me some peace of mind.

I‘ll update this thread with the final numbers are smart charging.

What do you mean by "health"? I always charge up any new battery before installing unless it's an emergency. And then I would make sure it's fully charged ASAP. Just sitting a week after a full charge and the voltage will definitely drop.
 

gathermewool

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What do you mean by "health"? I always charge up any new battery before installing unless it's an emergency. And then I would make sure it's fully charged ASAP. Just sitting a week after a full charge and the voltage will definitely drop.

I have a Foxwell battery tester. It‘s probably not 100% accurate, but is useful for comparison.

I drove home seven minutes away from Costco and immediately hooked-up my NOCO charger. I might hook up my power supply and run it at 14.4V for a bit afterward to see what the current is at that voltage.
 
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One cold snowy night I drove my Tacoma home and parked at the drive so I could clear snow. It started normally at work 30 minutes from home. When I went to move it probably 45 minutes later, it was so dead that the dome light didn't come on. Wouldn't take a charge either. I was suspecting a broken buss bar inside?
 
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