Why is my car eating batteries?
January 12, 2017 6:34 AM   Subscribe

I've had to replace the battery in my car twice this year and it looks like I need a third one. Help me figure out what's wrong before an expensive garage trip.

I have a 2006 Saab 9-3 (a fairly standard GM sedan with few Swedish eccentricities). For the first two and a half years, it worked great. The last year I've had endless problems with the battery.

- In January last year, it wouldn't start. The battery looked old (GM-branded, possibly factory original) so fairly quickly I went out and bought a brand new Bosch battery and everything worked great for a few months.
- In April that battery went bad. I took it back and had it replaced under warranty.
- In October the replacement started having the same problems. I've been using a combination of a boost starter and an old battery since then.

All three batteries have had the same problem - they won't hold a charge above about 11 volts, indicating one of the six cells is bad. Generally they've been at super low voltages (7 or 8) when pulled out of the car. Is this something that can be done by an electrical problem in the car - such as high parked drain, or alternator problems?

Have I just had bad luck with batteries - should I try my luck with a new one? I'm a bit of an electronics nerd - is there anything I can measure to see what's going wrong? Or should I just let the garage look at it?

The car isn't a daily driver. It gets used for one or two long trips a month plus a few errands. My attempts to measure the drain current when parked have been inconclusive due to the amount of smart electronics in the thing. I'm fairly certain the alternator is working, but haven't yet rigged up a way to check the voltage while moving.

Thanks!
posted by grahamparks to Travel & Transportation (24 answers total) 1 user marked this as a favorite
 
I had a car that drained batteries, and we found out that one of the retractable headlights had gotten partially stuck, and the motor that controlled it was, unknown to us at the time, constantly running to try to correct this, and it ended up draining the battery over and over.

Could something similar being going on with your car? Something is constantly running that you're not aware of?
posted by Hanuman1960 at 6:41 AM on January 12, 2017 [2 favorites]


What's the weather like where you are? Is the car subjected to extremes of temperature?
posted by yarntheory at 6:44 AM on January 12, 2017 [1 favorite]


I'm fairly certain the alternator is working, but haven't yet rigged up a way to check the voltage while moving.

The car doesn't need to be moving -- the alternator can't tell whether the car is in gear. Just check the voltage with the engine running. If you want to see what it does at varying RPM's then have someone give it a bit of gas while in park.
posted by jon1270 at 7:29 AM on January 12, 2017 [3 favorites]


A rough way to check the alternator is to measure the battery voltage when engine is off. Around 12 volts is fully charged, 9 or 10 vdc, the car will probably start if it is not too cold. When running, the voltage at the battery should be around 14 volts, indicating that the alternator is working.
You should probably try to run the engine at least once per week, more if it is very cold.
posted by H21 at 7:33 AM on January 12, 2017


The car is parked on street in the middle of London. The temperature rarely drops below 0 C and I don't think it was a particularly hot spring or summer.

The oddity here isn't the batteries going flat, it's them being destroyed beyond the point of being able to be recharged enough to start the car. Is that something anyone else has experienced?

(also my driving habits haven't changed since the first two years of owning the car, where I don't think I experienced a flat battery once)
posted by grahamparks at 7:46 AM on January 12, 2017


Can you connect your battery to a battery tender when you're letting the car sit?
posted by gregr at 7:46 AM on January 12, 2017


When this happened to me in an old Volvo 240, the culprit was that my alternator was overcharging my battery and destroying it. I went through about three batteries before the local Volvo shop figured this out.

I'm not sure as to exactly how or why this happened as I'm not a mechanic, but this was the diagnosis given to me by the guys at the shop. Also, this was over 20 years ago and my memory of the details may be a bit fuzzy. I do know that once the alternator was replaced, I never had any issues with the battery again while I owned the car.
posted by ralan at 8:00 AM on January 12, 2017 [6 favorites]


ralan: "When this happened to me in an old Volvo 240, the culprit was that my alternator was overcharging my battery and destroying it."

Yep, this is a classic voltage regulator symptom. An alternator putting out 14.5 volts or more when your battery is fully charged will boil off the electrolyte and damage the plates. A mechanic should be able to test this for you also (in Canada anyways) alternator rebuild places and some autoparts stores can test the alternator out of your vehicle. Most GM alternators have integrated regulators.

PS: you can just stick your meter leads in the accesory port if you want to test voltage while moving but as H21 said this isn't necessary in most cases to check alternator function which is strictly RPM and battery voltage level regulated.
posted by Mitheral at 8:11 AM on January 12, 2017 [6 favorites]


This went on for me in a 1986 pickup for 3 years before we finally discovered it was the starter motor, somehow pulling a trickle of power.
posted by buildmyworld at 8:33 AM on January 12, 2017


I had that problem, and it was my starter motor. Garage also told me an alternator problem could cause it. There's definitely an underlying problem, get it checked out.
posted by tinkletown at 9:38 AM on January 12, 2017


I was also going to suggest the voltage regulator (or whatever serves that function in a modern car).
posted by SemiSalt at 9:48 AM on January 12, 2017


I had this identical issue with my car. It turned out to need both a new starter and alternator. It was killing batteries by generating incorrect voltage and amperage.
posted by strixus at 10:03 AM on January 12, 2017


- In January last year, it wouldn't start. The battery looked old (GM-branded, possibly factory original) so fairly quickly I went out and bought a brand new Bosch battery and everything worked great for a few months.

It's interesting it had a GM battery because GM systems run at 14.5 V, Saab systems use 12.6 V, and the two are not generally compatible:
Due to the varying nature of car electrical systems, never jump start your Saab using another car that is running. Use the other vehicle's battery power alone to start it because a 14.5 volt running system (i.e., GM) can seriously damage a 12.6 volt system (i.e., Saab) due to the overvoltage.
So I agree that overvoltage is the problem, and I'd guess that someone put in the GM battery in the first place to deal with the very issue you are having.

It doesn't seem likely to me that a GM-style alternator and/or voltage regulator would even be possible to install in your Saab, but I would make sure my alternator and voltage regulator were Saab compatible.
posted by jamjam at 10:14 AM on January 12, 2017


The 2nd gen Saab 9-3 is a multiplatform GM product (Global Epsilon) with very little in common at the mechanical level with previous Saabs. Its OEM charging system is 100% GM.
posted by Mitheral at 10:34 AM on January 12, 2017 [1 favorite]


Any repair garage should be able to check your charging system and see if the alternator is working up to snuff. It's almost certain that you have a bad alternator.
posted by Thorzdad at 11:44 AM on January 12, 2017


Mine was the starter.
posted by WeekendJen at 12:21 PM on January 12, 2017


It's interesting it had a GM battery because GM systems run at 14.5 V, Saab systems use 12.6 V, and the two are not generally compatible:

This sounds rather suspect. Both GM and Saab are nominal 12V systems using the same batteries. For both, the fully charged, unloaded voltage is 12.6 volts. For both, charging is not possible below about 12.9 volts. For both, charging below about 13.5 volts would be inordinately slow. 14.5 volts will not damage a discharged battery but you don't want to hold a fully charged battery at that level for a long time. I doubt that any Saab cannot tolerate 14.5 volts for the length of time to jump start a car.

I would like to see more detailed documentation than just one web site. The Saab manuals I have seen describing jump starting don't make any special restrictions.

Perhaps they are confusing with the ancient Saab 92 family from the 1960s that had a 6-volt electrical system like the old VW beetles.
posted by JackFlash at 1:18 PM on January 12, 2017 [1 favorite]


That web page is from 2002 (according to Google's timestamp) and is probably referencing even older models than that. So I think it's a red herring. Interesting though.

Thanks all. I'm going to check the charging voltage while revving the engine and then take it down the garage and hope it's not too expensive.
posted by grahamparks at 1:42 PM on January 12, 2017


Saab 9-3 2005 owner here. Had a similar problem - went 3-4 several batteries over 3-4 years. I would also burn out headlights at a very similar rate. At some point I went back to the Saab-brand batteries and that seemed to help (~4 years ago), but I know I don't have a saab battery in it now and it's been fine for the past 2 years. I drive the car daily and have for years.

The light bulb thing magically sorted itself out - I think I had my non-dealer mechanic fix it for me and that's resolved it - they were unbelievably hard to install.

I'm also in the US. I don't think I've shed any light on this but me-mail me if you have questions.
posted by Farce_First at 2:40 PM on January 12, 2017


I've just done some tests. 12.7 volts off, 14.98 volts at idle. Revving the engine doesn't seem to boost it. Now to get it fixed...
posted by grahamparks at 5:52 AM on January 13, 2017


I think you have twigged to this, but 15V is pretty high.

This is a good writeup. Summary: need 13.8V minimum to start charging, ideal is between 14.2V and 14.4V and definitely below 14.7V.

Your alternator's voltage regulation is out of spec...
posted by no1hatchling at 7:04 AM on January 13, 2017


I tested it again when I got home but before I switched the engine off, and it was down to 14.3 volts, again not varying significantly with engine revs. Hmmm....
posted by grahamparks at 11:44 AM on January 13, 2017


The voltage shouldn't vary significantly with engine reving. That's the purpose of the voltage regulator -- to regulate the voltage so it doesn't vary with engine speed. It may drop somewhat at very low idle when the engine is hot, but at fast idle when the engine is cold should not be much different than high revs.

Charging voltage will vary somewhat depending on the battery temperature so the voltage may be slightly higher when the battery is cold and slightly lower when the battery is warmer. A battery warms when it charges so you may see a higher voltage when you first start the car and a lower voltage after driving for a while.

If over-voltage were killing your battery, you would see this as a decrease in the water level below the plates. Did you check that visually with the dead battery? It is rare for batteries these days to lose water. If you are losing water quickly, that is a sign of overcharging.
posted by JackFlash at 1:56 PM on January 13, 2017


I've been meaning to post an update to this. I bought another new battery (Lucas rather than Bosch) around the time I made this post and the car has worked fine since. I did eventually take it to the local Saab garage to have it checked out and they said 14.9 volts was the maximum allowable value, but still in spec. Which all points to the two Bosch batteries being duds, which is a bit surprising.
posted by grahamparks at 12:45 PM on September 24, 2017


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