I've been having issues with my 3 year old 12v battery over the past week. First time was my fault when I put air in the tires, using a cigarette lighter compressor, when the car was not in ready mode. The battery has drained 2 more times since then, both in very cold weather. Weather went down to 5 degrees last night & the battery is drained again. Couldn't start it this morning, and I noticed this evening there is a horn beeping noise coming from the engine. Is this a result of the battery draining, or could it be the issue causing the drain? I'm having a hard time getting the battery replaced because I'm being told the battery is good. Thanks for any advice. Will be purchasing a jumper and trickle charger for future use.
Well; if your battery was properly tested and came out good - You probably have a parasitic drain somewhere in your electrical system. You'll need to take it to an automotive electrical shop to diagnose that. In the mean time; someone that knows a bit of electronics should find the OBD2 plug for your car and follow that wiring harness back. Look for dealer installed alarms or trackers that may be malfunctioning, causing that parasitic draw on your battery. Remove it and see it that cures your issue. Good Luck.
who told you it was good? did they do a load test? draining these little batteries is often the beginning of the end, especially in the cold. you can get a free load test at most auto parts stores. has the battery been fully charged since draining?
AAA initially jumped my car after I accidentally drained it using an air compressor. The tech had a hand held device that showed the battery was good, Not sure if that qualifies as a sufficient test. They told me to drive it for two hours to charge, but the car was drained again the next day after very cold weather. I then took the car to Mavis (not my usual mechanic )and they also told me the battery was good, was taking a charge like it was new, and would not let me purchase a new one. Just a hunch, but I'm thinking the battery is not good, (1) because I had the same issue one year ago - battery died in my garage during extremely cold weather when it was only 1 year old. My mechanic kept it a couple of days and charged it up, no issue for a year, and (2) the current issue began when I accidentally drained the battery using a compressor, so I don't think it's a parasitic draw. It has drained 3 times the past week, and once last year. I have been reading up on battery sulphation and the effects on a drained battery.
Three years is not old for an agm battery in a Prius. A few discharges are not "that" bad for an agm. Measuring parasitic draw would settle the issue. No draw over 35ma, I would replace the battery. No one is going to refuse your request to buy a battery; however getting a free or discounted replacement requires a failed load test.
That AAA guy more than likely stated that "your battery is charging", because you can't load test a battery right after a jump start - it would fail because it's too low. You can't do that test until the battery is fully recharged; which is what your mechanic did when he kept your car for two days. That's a far cry from "your battery is good", then why did it need a jump??? Have you attached a battery charger to your battery, since you've drained it??? Have you had the battery tested after any of the three times you've drained it??? You can believe whatever you want and ask ChatGPT what to do; but unless you TEST - it's all speculation and won't solve anything.....
Do you drive it much? Short trips don't help. Over time, perhaps shortening the lifetime of the battery (I think, lol). The accidental drain didn't help. Cold weather brings out battery weakness. Even though only 3 years old, and maybe charging it up would work for a while, why not replace it? You're getting that battery jumper but who needs to get stuck in cold weather, messing around in the snow? If you could potentially get another 3 years out of a battery, I think it'd be worth the gamble. What do mechanics go for nowadays, $150/hr? I'm enjoying my new toy, a BM-2 battery monitor. It can even notify you on low voltage, so you can act before it totally dies.
You couldn't load test it per se after jump but ya can watch recovery of volts. After the event and things like that . Google how to setup fluke for parasitic drain 12v automotive it's really easy . Pull fuses slowly 2 at a time watch meter drop . That's the circuit that needs attention. Even if you can hand off car with this info . You saved yourself a few hours time in shop . Usually it's from poor installs of accessories.
The little electronic battery testers do NOT measure battery capacity. They do look for certain faults and can make a semi-accurate prediction of the short term current that the battery can provide. Unfortunately even a battery with only 5Ah capacity may be able to meet the CCA - it just can't do it for very long. The little electronic testers don't actually draw that sort of current, they estimate the CCA from frequency measurements on the battery. The Harbor Freight tester I have pretends that it can read Amp Hours, but it is clearly nonsense, since if you put in some random number on a good battery it will you a "reading" near that. The only way to get an accurate capacity measurement is to discharge the battery at 1/20 C (2.25A on the larger Prius 12V battery) until some predesignated voltage end point is reached. If the battery is working as designed it will take 20 hours to fully discharge one that started fully charged. (Lots of caveats, the main one being that the temperature should be a constant 25C.) If the capacity is reduced that voltage endpoint will be reached (much) sooner. The downside is that this sort of testing will damage an AGM battery, they do not like being fully discharged. I have been experimenting with a 2 hour discharge (at 2.5A, which is close enough to 2.25 so that the Peukert correction is small enough to ignore) followed by a 2 hour recovery. Here is the discharge curve for a brand new, fully charged Walmart S46B24R battery: IV discharge curves for a working Prius 12V battery? | PriusChat Dogma is that one should allow 24 hours for recovery. You can see from the recovery curve that it has a fast phase which is done in 2 hours. It may be that there is a much slower recovery mechanism that really does need 24 hours (at 25C) to complete. I have not yet done that experiment. Temperature is a big problem in these tests. I do them in the garage or the driveway, which aren't temperature controlled. So on a good day the battery can stay pretty close to 25C over four hours. Not over 24 though, any day of the year. Anyway, 4 hours is already quite a long test, and the battery needs to be isolated form the car to eliminate parasitic load during discharge and recovery. We can't easily speed this up, because drawing more current requires using the Peukert correction, and we don't know that factor for the individual battery, or even the battery model, and again, temperature matters.
I would not suggest it takes hours to properly load test a battery. I will agree the lowest cost electronic versions don't load enough or for adequate time. However an old school resistor based tester CAN accurately test. Typically they draw a 100 amps over a few seconds which separate the men from the boys. If it is vented it is resistor/ceramic or carbon pile based. Retailers and shops make warranty replacement decisions based on load testers . They don't take more than a few minutes. $22 or buy the same unit with a name brand for $46.
