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Battery Drain

Help, Advice, Owners' Discussion and DIY Tutorials on the Volvo S80 model. Sometimes called an "executive car", the S80 was and continues to be Volvo's top-of-the-line passenger car.
larzlo
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larzlo

Battery Drain

Post by larzlo » Sun May 31, 2020 4:13 pm

I have had ongoing issues with battery drain on my Volvo S80 for about the last two years. When I am commuting on a regular basis (~1:15 hour daily) there are no issues and everything works fine. The trouble starts when the car sits for a few days, then it becomes hard to get the car to start. After about a week of sitting without running the battery will be completely dead and I'll need to jump the car. With my inconsistent driving during this quarantine, it's been a real pain and I've finally decided to do something about it.

The most obvious answer is that there's some kind of parasitic drain. So I took my multimeter and measured the current draw across the battery. Multimeter read about 0.01-0.02 A which I understand is about normal when there is no load on the battery. I've tried measuring the current draw multiple times, before the car runs, after the car runs, always the same result, I'm not seeing any unusual current draw.

I've also tested the voltage of the battery and this is where things get a little weirder. After a long car ride (1:30 hour) the voltage on the battery was only reading 12.2 V, instead of the 12.6 V you would expect when it's fully charged. Two days later, measure it again, 12.0 V. Now I start the car (and it didn't kick on right away) and measure voltage and it's reading 14.3. That's a good sign because it means the alternator is performing as it's supposed to (I read you want to see 14.3-14.7 V). I turned the car off and measured the voltage across the battery again and it's reading 12.4 V. That doesn't make sense to me because there's no way the battery charged up in the short five minutes I had the car on.

The battery I'm using is only two years old and my dad claims he had it tested about a year ago (after these issued had already started) and the shop said the battery was fine. I'm still leaning toward it being a battery issue because it seems like everything else checks out. The next opportunity I get I'll swap my battery with another car's "confirmed good" battery.

Sorry for the wall of text but this one has been a real headscratcher. Does anyone have any other ideas of something I'm missing or something else I can test? Please let me know! Thanks in advance.

Cees Klumper
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Cees Klumper

Re: Battery Drain

Post by Cees Klumper » Wed Jun 03, 2020 9:14 pm

It sounds like the battery is the culprit, try the temporary swap. My batteries when fully charged sit at around 12.9 volts. If there's no parasitic draw to speak of I'd think it has to be the battery.
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oragex
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oragex

Re: Battery Drain

Post by oragex » Tue Jun 09, 2020 12:55 pm

larzlo wrote:
Sun May 31, 2020 4:13 pm
I turned the car off and measured the voltage across the battery again and it's reading 12.4 V. That doesn't make sense to me because there's no way the battery charged up in the short five minutes I had the car on.
That seems normal because right after driving the battery has some extra voltage that keeps lowering. A good battery reading is disconnect it after a drive, wait 1h then measure.

When you measured 12.0V that's indeed pretty low, have you tried removing the alarm siren fuse ?
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larzlo
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larzlo

Re: Battery Drain

Post by larzlo » Wed Jun 17, 2020 8:30 pm

oragex wrote:
Tue Jun 09, 2020 12:55 pm
larzlo wrote:
Sun May 31, 2020 4:13 pm
I turned the car off and measured the voltage across the battery again and it's reading 12.4 V. That doesn't make sense to me because there's no way the battery charged up in the short five minutes I had the car on.
That seems normal because right after driving the battery has some extra voltage that keeps lowering. A good battery reading is disconnect it after a drive, wait 1h then measure.

When you measured 12.0V that's indeed pretty low, have you tried removing the alarm siren fuse ?
So funny enough, my dad removed the #8 fuse about three years ago because I was having the infamous Volvo alarm siren issues (which it fixed), but your post had me double check just to make sure. I confirmed that the #8 fuse is removed, but I also found a 5A fuse in the #30 slot, which should have no fuse in it (and no systems associated with it) according to my owners manual. I imagine my dad just stuck the 5A #8 fuse in an empty slot for safe keeping. I'm now wondering if somehow this fuse could have closed a circuit, causing electrical issues. I read online that even though some of these slots are empty, they could have been intended for extra features and therefore can still be hooked up to the harness. Haven't had a chance to extensively run the car since, but I'll report back.

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