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Discussion Starter · #1 ·
Sorry, I couldn't help myself with the thread title lol.

We've all heard it before though, Subaru batteries are considerably mediocre. They don't like very cold starts, and they don't last very long.

Mine lasted about 21 months and 24,000 miles. The car was parked for about two days (Thursday and Friday) while I was out of town on work, came back and the car barely started. And I mean took three or four attempts to turn over, and I thought I was gonna need a jump, but I got lucky and it fired up. Drove about 50 miles home. I had no idea why it died, but it was 4AM and I didn't care.

Saturday afternoon I went to start it, and the same thing. It barely started. Didn't think much of it, I figured I would diagnose it later. Drove about 25 miles. Later that night, went to start it to drive home, turned over but would not fire. I had brought jumper cables just in case, so I had a friend jump me and I drove another 25 miles home.

Sunday I didn't drive the car, but I made an appointment to have it serviced on Tuesday (today). Went to jump the car to drive it to the dealer and it wouldn't even try to turn over. I tried an industrial charger pumping almost 50A into the battery and it did nothing. Called Subaru to ask if I could just bring in the dead battery and they said no, I needed to have Subaru Roadside Assistance tow the vehicle in. Of course. So I set up the tow, and in the meantime tried to swap in a battery from one of our other cars just to get it to start and drive to the dealer. The battery terminals weren't in the right spot though so I couldn't connect it. Original battery back in. Gave it one last shot on the charger, and it fired right up. Must've just needed a computer reset after having the battery die. Drove it to the dealer and canceled the tow. On the way there, the voltage was fluctuating all over the place. Anywhere from 11V up to 15V. I tried to keep the engine revs up at red lights to keep it charged so I wouldn't stall.

Got to the dealer right before they closed, they put me through Express Service, swapped the battery, "rechecked charging system, all ok" and I was off. Right after pulling out of the lot I noticed the voltage start to fluctuate again. This time anywhere from 12V up to 15V. Figured maybe it needed a minute to adjust to the new battery and stabilize. Got home, plugged in my ODB reader and set it up to log voltage and went back out driving. It fluctuated almost as much as my throttle input.

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A quick google will tell you that driving a car on a dead battery can kill the alternator. Guess what I did? Over 100 miles on a dead battery. The regulator/alternator is shot. Back to the dealer hopefully tomorrow top have it fixed, all under warranty of course. Hopefully they can squeeze me in, but I made an appointment for next week just in case.

TLDR;
Subaru batteries are junk. If your battery randomly dies, check it immediately and don't drive the car too far on it, even if you can jump start it. Even if your car is under warranty its not worth killing the alternator, it just causes more of a headache.

Also you may need to unplug your battery and reset the computer before it's willing to turn over.

And always double-check your dealer's work, cause they might say they tested your charging system when they really didn't, like mine did. Any decent mechanic would see that the voltage is not stable at 14.2V with the engine running, and know something was wrong.

And if your car is not under warranty, just buy a nice battery for it. It can pay for itself if your original battery would've died and taken out your alternator/regular with it.
 
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It is a good idea to put battery on charger overnight every few months. This keeps the battery topped up AND equalizes the cells.

Your vehicle alternator is NOT intended to charge a weak battery. It is computer controlled to maximize MPG.
 

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What Bruce said, plus this:

After many years fighting with Subaru batteries, and losing, when I got my last new Suby I knew it was no different. So I got a good battery charger figuring if it kept my battery alive for three years it would pay for itself. It did just that. My battery was always in great shape... for the low power 390 CCA lump it was anyway. But never an issue in three years.

When I got my new Imp the battery was dead when I got it but was told they'd replace it. Since it was 9pm by then I drove it home without shutting it off. At home I attached my trusty charger and let it run all night. The battery was still bad so I took it in for a new one. I left with their top battery, a good one for a change.

But I still hooked up the charger and let it do its thing. The new battery is great, and I feel confident it will remain so as long as I will likely own the car, at the least.

My battery charger does more than just apply a trickle charge like most such gadgets do. I use it at least once a week overnight. Like most things, there are better, but the cost of this one fit my purse.

It is a:
BatteryMINDer Battery Charger/Trickle Charger/Desulfator - 12 Volt, 1.5 Amp, Model 1500

IMHO, everyone should use a similar charger regularly. You won't have problems and it will pay for itself in the long run.

Or keep fighting a losing battle with batteries.
 

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Discussion Starter · #5 ·
Update:

Went back to the dealer today, they said they tested the alternator and everything is operating normally.

Logging the voltage with my OBD reader, it seems to be fairly normal behavior, ranging from 12.3V (base battery voltage) up to 14.9V (full charging level) depending on engine load, accessories on, etc. Sitting at an idle it is fairly stable.

For example, under light load it dips down into the 12’s, and when engine-braking it creeps up into the 14’s. Also under heavy load, when there’s power to spare, it charges high 13’s or 14+. This is consistent with what Bruce said, and I what I saw in some other forums, that the charging system is optimized for fuel economy.

My only question then, is why did I never notice this before?? I have been running a dash cam for over a year that has a voltage readout on the footage. It’s always been rock solid at 14.1-14.3V consistently. I got a new radar detector a couple months back that has a voltage readout, and it too was reading solid around 14.2V regardless of load or anything else. Even after my battery died and I jump started the car, it still read 14.2V steady after the first jump.

Just curious if anyone else has some knowledge of what the voltages of the charging system in our cars run? If I get a chance I will plug my OBD reader into another Gen5 Impreza and log the voltage.
 

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My only question then, is why did I never notice this before?? I have been running a dash cam for over a year that has a voltage readout on the footage. It’s always been rock solid at 14.1-14.3V consistently. I got a new radar detector a couple months back that has a voltage readout, and it too was reading solid around 14.2V regardless of load or anything else. Even after my battery died and I jump started the car, it still read 14.2V steady after the first jump.
Answer: The accuracy of those devices is questionable. I always use my $300 Fluke meter when I want accurate measurements.

I also have a plug-in voltage meter which goes into power-outlet (ciggerete-lighter plug) which can be used to monitor while driving. I got it from Walmart and validated its accuracy with my Fluke.

IMPORTANT: If you are seeing DIFFERING voltages in different circuits.... suspect a poor connection/ground somewhere. When there is a poor connection, the computer gets confused and will not command the alternator to turn on when it should.
 

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Discussion Starter · #7 ·
Answer: The accuracy of those devices is questionable. I always use my $300 Fluke meter when I want accurate measurements.

I also have a plug-in voltage meter which goes into power-outlet (ciggerete-lighter plug) which can be used to monitor while driving. I got it from Walmart and validated its accuracy with my Fluke.

IMPORTANT: If you are seeing DIFFERING voltages in different circuits.... suspect a poor connection/ground somewhere. When there is a poor connection, the computer gets confused and will not command the alternator to turn on when it should.
To your last point, the dealer told me when I brought it back that they found a loose connection on the battery terminal. I thought that may be the cause of the fluctuations, but after "fixing" that it still behaves the same.

While yes, the dash cam and radar detector aren't bonafide volt meters, they seem to be accurate with a few tenths, verified by my not quite $300 multi-meter. I noticed a 0.2V increase when I switched the radar detector from the cigarette adapter to the hardwire kit. Probably just means the cigarette adapter had additional line voltage drop through the extra long curly cord.

My OBD reader can read the voltage at the OBD port, and also read the "control module voltage" from somewhere within the car, I'm assuming this is what the car's computer sees. These two have been within a couple tenths of each other too.

Who knows, maybe I'm crazy and I just never realized the voltage fluctuating this much before?
 

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Answer: The accuracy of those devices is questionable. I always use my $300 Fluke meter when I want accurate measurements.

I also have a plug-in voltage meter which goes into power-outlet (ciggerete-lighter plug) which can be used to monitor while driving. I got it from Walmart and validated its accuracy with my Fluke.
Question: What did you find when you compared your instruments to the voltage readout on, say, a RD?

I have a Fluke, too. I've compared them and find the reading on my RD to be within a few tenths... close enough for me considering the convenience factor.

FWIW, I am rather anal about such things... having spent my working life in many facets of electronics. I even had a dedicated, accurate, voltage monitoring module on my motorcycle years ago. But voltage monitoring is just the beginning.

A reliable voltage system is imperitive to a vehicle. That's obvious. What I find almost invisible, to most, is the "dark side" of that moon... resistance. Specifically sub-ohm resistance in the ground system... starting with the battery's but includes the entire ground system. Grounds are just as important as what everyone focuses on, voltage. In fact, the actual work that voltage does, through current, depends on grounds even more than voltage. Also, a variety of components like injectors, ignition, MAF, etc, depend on excellent grounding to eliminate inter-system signal conta mination..

It's amazing and a little alarming to see (via a good scope) the spurious signals of unrelated components' signal spikes riding on the output of another system. The designers deal with that problem with filtering these days. But filtering can only do so much. A compromised ground at any point in the ground system can affect an engine's operation in ways that are baffling and very difficult to diagnose. Ensuring the integrity of grounds, like the battery condition discussed here... is rarely important to the motoring public. Until there's a problem. I prefer preemptive maintenance, myself.

The interconnection of systems via connectors is a subset of the subject. Same usual result... ignored until a problem, and another one difficult to pin down. And here again the solution is simple: preemptive maintenance. That is, not only making sure all connectors are securely fastened, but also ensuring they're protected against deterioration by environment influences, specifically water. An easy and simple application of the proper weather protection to the contacts inside the connectors all but eliminates future problems.

All this to say... preventive maintenance is one of the easiest and most important ways to keep your automotive investment working for you.
 

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To your last point, the dealer told me when I brought it back that they found a loose connection on the battery terminal. I thought that may be the cause of the fluctuations, but after "fixing" that it still behaves the same.

While yes, the dash cam and radar detector aren't bonafide volt meters, they seem to be accurate with a few tenths, verified by my not quite $300 multi-meter. I noticed a 0.2V increase when I switched the radar detector from the cigarette adapter to the hardwire kit. Probably just means the cigarette adapter had additional line voltage drop through the extra long curly cord.

My OBD reader can read the voltage at the OBD port, and also read the "control module voltage" from somewhere within the car, I'm assuming this is what the car's computer sees. These two have been within a couple tenths of each other too.

Who knows, maybe I'm crazy and I just never realized the voltage fluctuating this much before?
Assuming your wiring is good, the fluctuations are, at least to me, explainable by the way the alternator's voltage control works. The computer runs it using a variety of inputs on a continuing basis, so the varying signal to the alternator's voltage regulator result in a varying output.

When I finish some ongoing projects I'll look at mine. If I see the same thing or something different I'll update the thread.

I like the way you think. :)
 

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It is not the 'fluctuating' voltages which I refer to. (This is normal operation of the computer attempting to unload the engine by turning off the alternator)

Also, to confirm what Chrystal Imp said when I talk about "poor connections" I am talking about the ENTIRE circuit. (including the grounds) Infact, it is poor grounds whcih can REALLY mess up the operation of the electrical system because everything else is based on the assumption that ground is within 10mV of battery-negative.
 

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Discussion Starter · #11 ·
Yeah after driving it for a couple days the behavior seems to be pretty normal. Just not sure why it wasn't doing it before, maybe my old battery was just so mediocre that the alternator needed to being charging on high constantly just to keep the voltage up.

However, now my problem is my radio's DSP Module, the Rockford Fosgate DSR-1, which doesn't like the voltage spikes. It keeps cutting out momentarily when the voltage surges up to 15V after letting off the throttle, and turning back on which sends pops through my speakers since my amplifier doesn't care and remains on the whole time. Investigating a firmware update for the DSR-1 that might address this, or worse case scenario look into adding a capacitor in front of the DSR-1 to smooth things out. This is an issue I had on rare occasions with the old battery, but I thought it was just a loose connection on my part during the install. (That could be a whole other thread but I'm too lazy. Might update my stereo build thread if I end up changing anything.)

It's always something with a modified car!
 
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