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I recently had my car in for servicing for a front end problem (turned out to be some loose lug nuts), but as part of the service they checked the battery and said that the battery was in good shape, but slightly low on charge. They didn't look into it at all since it wasn't bad enough to worry about and that wasn't why the car was in anyway, but the technician was saying he was thinking this model *might* have an alternator that was designed only to maintain the charge of the battery, not recharge it. He really didn't know  without looking into it more though.

 

Was he right in his guess, or might it be something else causing a low battery, such as an alternator going bad? For what it's worth, I haven't had any issues, including when starting at the -47º temps we had last week, so while the charge might be a bit low it's not enough to impact performance, at least not yet.

Edited by ibrewster
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All charging systems are designed to bring the battery back to full charge.  That being said, at -47 in Fairbanks, you are running the electrical system really hard:

- Hard to start at low temperature

- Lights on all/most of the time

- Defrost/heater blower on all/most of the time

- Rear defogger on all/most of the time

- Battery is cold so it is harder to charge.

 

A battery blanket might help, or put the car in a warm shop for a few days to get warm, then take it on a good long run with as little load on the electrical system as possible, and the battery should charge right back up.

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Yeah, I have a battery blanket which is plugged in all day when I am at work, and over night the car is parked in a nice, warm garage that I just got this year (it's lovely). Also, the -47ºF was last week - today it's only around -13ºF, so not so bad. That said, it probably did get a fairly good drain starting at the lower temps, even with the battery blanket, and the rest of what you said about load is certainly correct (don't forget the heated seats!), so it makes sense that it should get back up to full charge here shortly. Thanks!

 

P.S. What's your idea of a "long run"? My idea is the 6 hour drive down to Anchorage, but I'm sure that would be overkill. Would the 15 minute drive to/from work count? :)

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I would say that 15 minutes is not enough.  The car will be barely warmed up.  And you will be doing that with full load on the electrical system.   Six hours to Anchorage is overkill. 

 

An hour in the middle of the day would do it, especially if you get the car warm enough to turn off all the power-sucking accessories, and started with a warm battery.  2 hours would be tons.   So consider a Saturday sight seeing trip, there has to be somewhere worth going to around Fairbanks besides Anchorage.

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Good advise from those who posted above. I would also suggest when your car is in the warm garage to put the battery on a battery charger over night, when outside temp is below zero. Don't need doing this daily, maybe a few times per week to make sure the battery stays fully charged. The battery charger will stop charging, when battery is fully charged.

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I don't recall the exact age of the battery - I did have it replaced, *I think* about two years ago, but I don't recall exactly (I'd have to dig out the records). Regardless, the shop tested the battery, and they said it was in excellent condition, just low charge. As for the alternator, it is original equipment, so around 43,000 miles.

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Nothing wrong with it besides just being flippin COLD out there!

Batteries don't produce as much current in cold weather. The chemical reaction that creates the flow of electrons can't happen as fast when it's cold out, and that goes the same for re-charging once the engine is running. It takes longer for the battery to recharge when it's far below freezing temp.

 

A cold battery can show a very low state of charge on a tester even though it's totally fine.

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Yeah, they did do the testing in a garage, but perhaps it hadn't been inside long enough for the battery to fully warm up. I guess as long as my car continues starting properly (which, so far, it has), I won't worry about it too much. Maybe recheck this summer.

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Get yourself a battery maintainer that you can connect directly to the battery and just disconnect it via a plug.  The maintainer will put a trickle charge onto the battery as long as it is plugged into a 110v outlet. 

 

You could also wire it to where it is plugged in when you have your battery warmer plugged in which will help the battery out a whole lot.  Here is what I ran on my 98 Outback and a diesel truck here in Colorado. 

 

https://www.amazon.com/Morange-MBC010-Battery-Charger-Maintainer/dp/B010NRKERI/ref=sr_1_13?ie=UTF8&qid=1485373194&sr=8-13&keywords=battery+maintainer

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Get yourself a battery maintainer that you can connect directly to the battery and just disconnect it via a plug.  The maintainer will put a trickle charge onto the battery as long as it is plugged into a 110v outlet. 

 

You could also wire it to where it is plugged in when you have your battery warmer plugged in which will help the battery out a whole lot.  Here is what I ran on my 98 Outback and a diesel truck here in Colorado. 

 

https://www.amazon.com/Morange-MBC010-Battery-Charger-Maintainer/dp/B010NRKERI/ref=sr_1_13?ie=UTF8&qid=1485373194&sr=8-13&keywords=battery+maintainer

Thanks. Simple, cheap, and many people do say that trickle charging the battery is better than simply warming the battery, so probably better. Did you leave that connected to the battery all the time, or only connect it when needed? I'll have to get a larger splitter for my plug-in cord, since my current three-way splitter is full with battery blanket, freeze plug, and oil pan warmers (I think - could be wrong about the specific devices, as I didn't do the install).

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I would plug it in when my vehicles are in my unheated garage.  My diesel truck only gets ran about once a month and it keeps the batteries (two of them) fully charged with no problems.  I sold my outback but when I had it I would leave it plugged in as long as it was in the garage which at times extended to a week or so.  I used the eye terminals and connected them directly to the batteries and then ran the plug out under the hood.  Different vehicles will need to be connected differently since the cord length that attaches to the battery might be too short to come out from under the hood.

 

They don't draw that many amps so if I was you I would arrange the plugs to where the battery maintainer was on whenever I plugged it in when in the garage overnight to fully charge the battery every day.

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