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So today I monitored voltages while driving. Initially the car charges the battery at 14.3 volts, but as the car warms up, it stops charging and stays at 12.5 volts at idle. If I press the rear defroster button it jumps to 14.3 volts.

Does anyone know if generally, for short trip use, an AGM or a flooded battery would be better?
 

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I think the AGM battery is possibly the better choice but I have found that AGM batteries tend to fail without much notice.

I have recently purchased a digital battery checker which tests the battery and compares the rated CCA with the actual CCA so you can get an actual assessment of the “health” of the battery. I plan to use this tester each time I service a vehicle so I can hopefully get advanced warning of a potential battery failure.

By the way I think the Amps a battery is accepting at various times during a drive cycle is more important than the voltage of the battery (although the voltage and Amps may be related).

An alternator should put out enough Amps (just after starting the engine) to quickly replenish the Amps used to start the engine. As the battery is replenished the alternator output drops accordingly. This may be why the battery voltage reading starts at 14.3 and then drops to 12.5 later on.

Seagrass
 
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It seems very odd to me that the voltage measured by SilverOnyx would ever drop to 12.5 volts with the engine running. It makes me think that the alternator current output at idle (fully warmed-up "low idle") is lower than the electrical demand at that time. But then it is weird (or contradictory) that the voltage comes back up to 14.3 volts when the rear defroster is turned on (which significantly increases electrical demand). It makes me wonder if the alternator is designed to be some sort of "smart" alternator, that turns off its own output if electrical demand is low, presumably for the purpose of reducing alternator mechanical drag, when its electrical output isn't actually needed?

Normally, I would expect something like 14 volts whenever the engine is running, with an adequately-sized alternator.

(As a side comment, in the old days of generators, versus alternators (like on 1950's and some 1960's cars, and older), generator output would be quite low at idle, to the point that you could see your headlights dim a bit at idle... But alternators have good output at low rpm.)
 

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... It makes me wonder if the alternator is designed to be some sort of "smart" alternator, that turns off its own output if electrical demand is low, presumably for the purpose of reducing alternator mechanical drag, when its electrical output isn't actually needed?

Normally, I would expect something like 14 volts whenever the engine is running, with an adequately-sized alternator. ...
Yeah, basically that.

In my understanding the readings of >14V are when the alternator is supplying additional current to the battery. In my older vehicles with less complicated electronics, >14 V when the engine was running was normal. 12.6V across the anode and cathode on the battery when the engine is off is fully charged.

So today I monitored voltages while driving. Initially the car charges the battery at 14.3 volts, but as the car warms up, it stops charging and stays at 12.5 volts at idle. If I press the rear defroster button it jumps to 14.3 volts.

Does anyone know if generally, for short trip use, an AGM or a flooded battery would be better?
In my experience, the real benefits to an AGM battery over a flooded or extra-fancy flooded (whatever the silly designation is for the flooded batteries with thicker plates) is the quasi-sealed nature of the thing. The physical case.

With respect to consistency of voltage and reserve capacity AGMs are purported to give superior performance. I suppose that's probably accurate? More controlled gas exchange and different rates of sulfation as a result, I reckon.

The superdope batteries I saw were proper sealed lead acid batteries. Big [email protected]#*-all AGM 8D 160+ kg jobs for motorhomes, buses and whatnot. One could run all sorts of goodies for a few days off those. I think they're also used to start diggers and graders? I was thinking about using those for standby power for the home. I got a generator instead.

If I could find a decent, properly constructed AGM that fit the compartment correctly and was manufactured to tolerate the stop-start doodad I'd snag one. I was thinking this or this.

I remember when they named these after Decepticons.

From page 532 ze mothership says LN2. According to this there are three product options. Looks like the 47PG is the model with the highest CCA and reserve capacity. My apologies if that's already been posted. ****, I might have stolen from this thread. I'm dumb.

In terms of short trips- I'd guess we're boned. Whatever battery is in there, alternator needs time to charge the simple thing. I picked up one of those ctek charger/condtioner doohickeys you mentioned upthread. I'll slap that on there occasionally. I'm also going to use it for the little SLA starting battery in the generator.

On an unrelated note the softwarenanny500™ for the forum automatically made my no-no bad language word into asterisks. Dope. 🧐😎
 

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Oh yeah; got distracted. I forgot why I posted. I'm dumb.

So my battery discharged to <3V the other day in August; I'm dumb. I probably didn't close the door as to maximize dumbness. Had to use the key to open the door like some sort of numpty from the Pleistocene. I jumped it and drove for bit and it charged right back up.

The interior warning lights for eyesight and the rear braking monitor tripped. I looked that up in the manual; short answer is "you're boned, go to dealer for service."

I used the satellite doohickey service to speak to a nice young woman who answered. She assured me that the interior warning lights would go away. They did- dopeness abounded.

The app on my phone, however? Oh it is displeased. Its disappointment and chagrin can't be overstated. My car emailed me. I am Dumb Batman; my car emails me to alert me to things that are not copasetic. The app itself scolds me every time I log in. My behavior is reprehensible; I have no excuse.

A Subaru dealer called me about a week after the battery discharge. I didn't call them. The automated and integrated systems selected a dealership and their service department called me directly. I'm a bit conflicted. On one hand, that's supremely convenient as all get-out. On the other hand from what I've read here dealer service is often akin to getting to know rhinoceroses in a biblical sense.

In the past, I've used dealer service centers on other vehicles from different manufacturers when I had to. Like I said, not always fun. "Bring crisco," is what I tell myself.

My guess is that the Eyesight and RAB systems are fine. The fault code is probably being stored on the car and is being uploaded through the Starlink system, yeah? Codes getting stuck is still a thing, right? I heard folks with actual experience working on cars saying that? I'm dumb. One of those ODBD 2 thingies could potentially solve that, maybe? Thing is- I read here (probably) that those devices can interfere with Subaru's implementation of whatever standard those devices read and Starlink. I have zero knowledge of this junk.

I called a local import-friendly mechanic who's well reviewed. He seemed confident he could make the bad noise go away. He laughed when I told him about my car emailing me. I still do.

Honesty, I'd rather err on the side of caution and have it all resolved correctly. Make the app love me again, and all the status reports and monitoring records go back to green across the board. But with the pandemic, I am not stoked on having the car worked on. I figure let it sit for three days after anyone interacts with the car to disinfect the cabin.

That leads to the question of having that done at a local dealer for the service or go with the local cat.

Anyone have any ideas?
 

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Many dealerships are somewhat inept with all the new-fangled stuff as well. It took mine 6 months (not exaggerating) after 4 attempts, to clear a warning from my system for a service campaign update which the dealer performed but the app did not register it as being completed. (WUU06 I think).

Even if your local mechanic fixes any actual problems with the car, the app will not know, and unless your mechanic has access to those dealer-only accounts that can input data to the central computers that inform Subaru of what has been done to your car, then it could be that your warning will remain persistent depending on what it is.

So in my opinion you're somewhat forced into a shotgun wedding with the dealer for certain things. Since you're under warranty I would presume they wouldn't charge you for these services?
 

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Last night I fully charged the battery. Immediately after taking it off the charger, I started the car and noticed that on ignition (my battery voltage monitor is on a switched 12v outlet in the console) it showed 14.3 volts, but within 2 miles of driving when I came to a stop, with the engine idling (start/stop had not kicked in) it went down to 11.95 and headlights were not on, but the A/C blower was at full blast.

I don't know if the car is somehow purposely draining the battery, or the 12v socket is somehow modulated, or if the battery or its connections are that bad. I also noticed that after I parked with engine still idling, occasionally the voltage reading would spike to 16 volts for maybe 1/4 second at a time.

Almost regret buying something to read real-time voltage from the socket. If I cared enough I would do a direct wire to the battery. :cautious: After parking the car, under the hood voltmeter with the engine off reads a decent 12.54
 

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I don't know if the car is somehow purposely draining the battery, or the 12v socket is somehow modulated, or if the battery or its connections are that bad.
Put the car in dealership mode kind of like we did when we needed to do the 504 software update. There is an option in one of those menus there to watch the battery voltage directly as the car sees it. It varies like that on mine as well so you're probably getting the correct reading
 

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... the 12v socket is somehow modulated ...
There's the rub; those "12v" outlets' output are constantly going to be fluctuating under normal operating conditions. Hundreds of mV or mA of variation is almost a guarantee.

Car power is a bag of hurt, I've been told.

The output from the vehicle's alternator is going to be constantly fluctuating even without all of the fancy doodads and whatsits we have running in these things.

Almost every sensitive piece of aftermarket electronic equipment I've seen in a vehicle needs either to be connected directly to the vehicle's power plant with appropriate purpose/application-specific voltage and amperage regulators or run through a discrete inverter with some sort of power normalization and "filtering" combination.

FYI: I am neither an electrician nor particularly intelligent. I am however a certified Some Guy on the Internet™.

Big ol' hunks of rock salt and all that.
 

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I own a 2015 Outback, we are the champions of battery problems. Over the years I have learned a lot about modern car electrical systems. In short, unlike much older cars, new cars do not have the alternator charging the battery 100% of the time. When the alternator is charging the battery, the voltage is greater than 14 volts. A battery that is fully charged and not being charged by the alternator is 12-12.5 volts. The electrical system only turns on the alternator when the battery voltage goes down to a certain level. Then it starts charging the battery again. This is done to improve MPG. While this improves MPG, it is not good for the battery. So be prepared for more battery replacements. I am on my third battery in 5 1/2 years and 60,000 miles.
 

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A full battery is at 12.6-12.7V.
At 12.0V, the battery is at below 50%. You do not want to go much lower than that to avoid damage.

Yes, Subarus seem to have battery issues.
 

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... At 12.0V, the battery is at below 50%. You do not want to go much lower than that to avoid damage. ...

Yeah- when I borked mine down to 3V my dumbness guaranteed I'll need a new one sooner. The battery charged and is functioning correctly, which is dope. Is PEBCAK applicable to cars?
 
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