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Testing the health of 12v battery?
- Thread starter OldPro
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RayK
Active Member
Nothing appears on the car's display regarding the health of the 12V battery until the system determines something is amiss. You could buy a 12V battery monitor (bluetooth enabled to communicate with your smartphone) and keep track of the voltages yourself but I can't tell you exactly what voltage or what prior history is needed to be measured for you to be concerned about replacement.
My understanding is that recent software updates have gotten better at predicting the failure of the 12V battery and that in most cases, you won't be stranded by a "sudden death".
For me, I took a proactive approach and replaced my 12V battery before its 4 year anniversary (and 23K-something miles). I never saw any message on the screen, nor encountered any "weird" events that may have been a precursor to failure. It was worth the ~$130 to me to replace it as I was going on a fairly long trip and I subscribe to Murphy's Law.
My understanding is that recent software updates have gotten better at predicting the failure of the 12V battery and that in most cases, you won't be stranded by a "sudden death".
For me, I took a proactive approach and replaced my 12V battery before its 4 year anniversary (and 23K-something miles). I never saw any message on the screen, nor encountered any "weird" events that may have been a precursor to failure. It was worth the ~$130 to me to replace it as I was going on a fairly long trip and I subscribe to Murphy's Law.
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spsheridan
Member
No way that I'm aware of for proactively checking 12V battery health. After only a year of buying the car, I got a warning that my 12V battery had degraded and it was time to replace it. I took it to a service center and they replaced it free of charge. So In my case, no sudden death and things worked out, but I wasn't pleased with a battery failure after only one year of use. Probably a defective battery and/or a premature failure of some sort.
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If your 12v battery is of the older, sealed lead acid family, testing it is fairly straightforward. There are many good testers available at reasonable price that allow you to put a load on the battery and get a gauge of its health. The better testers will also measure internal plate resistance and I find that the best measure for assessing decline and predicting failure.
The newer 12v Lithium batteries are generally better batteries (I'd argue that SLA is still a better option in very cold climates). But their properties of decline over time are different from SLA. You can buy monitors which track voltage, but that doesn't really tell you anything about the overall health of the battery. I don't know of an affordable tester that does (witness the numerous discussions around Tesla's BMS... a quite sophisticated system).
The newer 12v Lithium batteries are generally better batteries (I'd argue that SLA is still a better option in very cold climates). But their properties of decline over time are different from SLA. You can buy monitors which track voltage, but that doesn't really tell you anything about the overall health of the battery. I don't know of an affordable tester that does (witness the numerous discussions around Tesla's BMS... a quite sophisticated system).
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Yeah... there is SUPPOSED to be a notice, but many (many) times the car doesnt generate one for the older lead acid battery. So "not needed" is up to you, but I can tell you for a fact that not every car with the regular lead acid battery will generate a pop up before it fails. I can point you to several threads here proving that, so telling people definitively they will get a popup is wrong.
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stopcrazypp
Well-Known Member
That is useful information, but unfortunately does not tell you the LV battery health. I think to really do that, you need an external tester, which is how it is traditionally done for lead acids.
As others mentioned, Tesla does have a 12V battery failure prediction algorithm built in and a system to warn of it, but it has failed people plenty of times (plenty of threads on it). Certainly far better than nothing, but not 100% reliable either.
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jdcollins5
Member
I test my 12V battery just like I have tested my battery for years. After sitting overnight, test the battery voltage at the battery terminals. A good battery should be in the 12.5-13.5V range. If it is less than 12.5 it is marginal and if less than 12.0 it needs to be replaced.
For the Tesla, you want to do this without waking the car, which will pull in the HV contactors and the DC-DC converter which charges the battery. The best way to do this is to leave the Frunk unlatched. Leave your phone key in the house. Open the Frunk and test the battery voltage at the terminals with a Voltmeter. See the voltages above to determine battery health.
For the Tesla, you want to do this without waking the car, which will pull in the HV contactors and the DC-DC converter which charges the battery. The best way to do this is to leave the Frunk unlatched. Leave your phone key in the house. Open the Frunk and test the battery voltage at the terminals with a Voltmeter. See the voltages above to determine battery health.
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My vehicle has under 6000 miles. I had no issues until I had to park my car at the airport for a week. Not in a covered stall. When returning my battery was very low. I couldn’t update. Numerous alert warnings in car. Tesla service rep said “ it’s about time” and normal to replace the aux. battery at this age. She said if car was driven more the battery would last longer. So a $70 battery ( at a car parts store) will cost me over $ 350.00 to have it replaced at Tesla. So, tell me again on how I’m saving money not having to buy gas???
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Last I heard, a model 3(and presumably Y) battery of that era was only like $80 at the dealer and another $50 for a service ranger to install.
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Service Ranger is a person that comes in a small Tesla van and can repair your vehicle in your parking lot.
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stopcrazypp
Well-Known Member
Maybe your state is different, but the 12V battery in California is about $85 and labor to install $25-50.
And where can you find a 51R battery with a vent hose port for $70? It's more on the order of $200 (as most of the available ones are AGM). Even a conventional vented battery is well over $100, so Tesla's OEM battery is by far the cheapest option available. You can fault Tesla's parts cost for other items, but their 12V battery really isn't one of them.
How old is your car to need a 12V battery replacement under 6000 miles and not covered under warranty? If you still have warranty, it should be covered under warranty.
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