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Volvo 850 (after being rear-ended) drains battery and shows bad battery (after charging on battery maintainer)

Hi, I am not very well-versed with cars, but I have a 10-month old Interstate battery for my Volvo 850. About a couple of months ago, I got rear-ended while stopping at a red light to turn right. There was not much noticeable damage. However, the battery drains. So, I thought that maybe the alternator is bad and got a battery maintainer. This charges the battery up for a while but then it shows red (bad battery). This has now happened a few times. So, I was going to take it to the battery place to see if the battery was bad, but then the car would not start at all (multimeter reads 8.5V). I put it on the battery maintainer and checked about 3 hours later (the maintainer was yellow, which means still charging), however the multimeter read around 12V. The battery was charged and the car started. So, I decided not to take it to the battery shop because they would probably find nothing wrong with it. An hour later, the multimeter reads 9.5V. What could be wrong? I have no external after-market part on the car, the lights are not left on, etc. What I don’t also get is how the maintainer can charge and then read red: at this time the battery reads around 8V or so. Thanks for any suggestions/help.

This would possibly be as the result of the accident. A shorted out wire etc, do all your brake and tail lights work normally?

Hi, my battery is 10 months old, and still under warranty.

Yes, the brake and the tail lights appear to work normally. How do I figure out the shorted out wire or not? Thanks again!

Measure the draw as you pull fuses, my way, not a real mechanic, just a hillbilly repairman.

My bad. I misread 10 months as 10 years. It’s possible there’s a short somewhere but it’s also possible you just had some bad luck. Take the battery out of the vehicle and try charging it. If it takes a charge the problem is somewhere else, if it doesn’t the battery is bad.

That is more than I am, so I am happy to get your advice, thank you. So, I pull fuses and keep measuring the battery voltage using the multimeter? What am I measuring, sorry?

Perhaps this will help.
http://www.nissantechnicianinfo.mobi/htmlversions/Winter_2012/Parastic_Draw.html#:~:text=Each%20device%20with%20memory%20has,run%2020%20to%20120%20milliamps.

Thanks, no problem. I think that I will figure out how to disconnect the battery and do as you suggest. I read somewhere that a collision can damage a battery. However, it was not that big a rear-ending event, and I did not give much thought to it then, but the draining problems started shortly after that.

Thanks! My multimeter is analog, do I need to get myself a digital multimeter?

I do not know your multimeter, just check the options. I still remember a vtvm, vacuum tube volt meter.

Here is my multimeter. https://www.gardnerbender.com/en/p/GMT-312/5-Function-Analog-Multimeter
I have had it for a while.

Does everything electrical on the back of the car still work, trunk release, rear window wiper, rear window defrost ?

Thanks, btw, I forgot to mention, this is a 1997 850 sedan. Everything electrical on the back of the car works (trunk release, tail lights, fog light, reverse light) but I can not figure out how to tell if the rear window defrost is working or not. The battery still reads 8.5V (2 hours later from 12V) but the car will not start. All other lights work. I will let it sit tonight and report the battery reading tomorrow morning. After that, I will try out davepsinbox_157004 and Barkydog’s suggestions. Can a battery be such that it charges and then loses charge (from 12V -> 8.5V) while it is on the maintainer (though this afternoon, I had taken it off the maintainer in the half hour that this happened)? Many thanks!

Is that 8.5 volts down from 12 with one of the battery cables disconnected?

For what it’s worth an analog meter will work fine.

Something to consider is that the impact could have ruined the battery by causing an internal short or by dislodging a plate.

Does this battery have removeable caps on top? If so, you might disconect a cable and charge it for an hour or so… Then with the battery cell caps removed stick the meter probes into 2 cells starting on one end. You should see a reading of 2.1 volts. Keep moving the probes down the row of cells one hole at a time. All should show 2.1 volts. If one is off then there is a problem with the battery for sure.

That is a test for a bad cell only. Replace caps, allow the battery to sit for few hours and then test the total voltage. A good battery will stay in the 12+ range.
This is kind of a backyard testing method but it works.

Thanks, the battery may have gone down by no more than 0.2V. The battery is still connected to the car. So, it goes down from 12V -> 9.2V (in one hour) and from 9.2V to say 9V (in 15 hours). Note that I misread yesterday, it was 9 and not 8.5V. Is this evidence of a bad battery or a parasitic drain? (Of course, it is also possible that the rear-ending had nothing to do with this, or simply accelerated whatever process it started). I am not sure that the battery warranty is valid if I take it apart to check. It is an Interstate Battery (10 months old).

A discharged battery will read 12.0 volts, a charged battery will read 12.6 volts.
It will take 3 days to charge the battery with a battery maintainer, 4 hours with a battery charger.

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It is not easy for me to tell whether it is 12V or more than 12.6V, I guess I should get a digital multimeter then. But I have left it charging for days and eventually, the maintainer/charger light turns red (“Bad Battery”) and then the voltage shows on the order of 8.5-9V. The battery is attached to the car, so can this be owing to a bad battery or a parasitic drain?

We had a windstar that had a faulty brake light switch. The lights would stay on ending up with a no crank. I am not sure how dead the battery was but the 12 amp battery maintainer would charge it enough to start in 25 minutes or so.

And would it go down if you left it on the maintainer? (If so, this sounds like may be my issue, however, the lights are not on. But of course, could be lots of other things that do not light up in the car.)