12V Battery - How low can it go?

[TonyM]

My 2021 Toyota Corolla hybrid has a small 12V lead-acid auxiliary battery, and a larger high voltage traction battery. The 12V battery powers systems such as the audio, headlights, remote door locks etc. The high voltage battery is used to start the combustion engine and drive the electric motors.

Immediately after a drive the 12V battery sits at around 12.4-12.7V but this falls quickly to 12.2-12.4V. After being left overnight the voltage often falls below 12V. One morning last week I observed a reading of 11.3V when unlocking the car which triggered one of my dashcams to start recording.

The car doesn't use the 12V battery to start the combustion engine. But if the voltage drops too low the car is unusable - I can't lock or unlock it, and the ignition system will not function.

The car had its annual health check recently and there were no issues. I bought a battery tester last month and it says the battery is in good health.

I currently have my dashcams / hardwire kits set to 12.0V cutoff, and I have 12.2V as the hybrid parking mode trigger level on the A329T using the HK6.

Should I be concerned if the voltage drops to 11.5V? 11.0V? I think trip to the Toyota dealership to ask some questions might be worthwhile.

 

[Finnegan]

I don't blame you for being concerned. Testing the battery yourself was a good idea, but I have read
mixed reviews and results about various battery testers. Many folks seem to prefer an "old world" type
of battery tester sometimes referred to as a "toaster", because it draws 100amps to heat wires inside,
wires that glow like in a toaster. There will also be an analog meter to show the condition of the battery.

I don't know where to tell you to find one in the U.K. Here in the US I can find one at Amazon, or a place
called Harbor Freight.

All that said, anything over 3 years could be considered a "gift" on battery life. Too many things drawing
power while OFF. If yours is original it might be time to replace it anyway. Winter is coming and it might be
a bad time of year for your battery to fail you.

This is the Amazon/USA link to the tester I spoke of: https://www.amazon.com/gp/B0D2N8F3L4

 

[lufa6977]

Before my retirement, one of my responsibilities was DC power plants and Diesel Generators as backup to commercial AC. Experience taught us that 'toaster' type load testers were best avoided. They put unnecessary strain on a battery and were more prone to damaging it than not. It is better to test a car battery with an analyzer that measures capacity percentage, life span, internal resistance, cold-crank amps, etc.

For what your battery is dropping in voltage, it could be well dated and past its prime, or you may have a parasitic drain you are unaware of.

Once a month, I put a CTEK charger on my AGM battery and condition it. I am lucky in that I have a garage and can do so without fear of the charger or the battery 'wandering off'.

 

[Finnegan]

Before my retirement, one of my responsibilities was DC power plants and Diesel Generators as backup to commercial AC. Experience taught us that 'toaster' type load testers were best avoided. They put an unnecessary strain on a battery and were more prone to damage the battery than not. It is better to test a car battery with one of the analyzers that checks for capacity percentage, life span, internal resistance, cold crank amps, etc.

Thanks for your thoughts!

My only experience with automotive batteries is replacing one of mine when it fails. And I have the battery tester I linked
above, but have never used it myself.

Perhaps taking the vehicle to the dealer or other, with reliable test equipment, is the better idea after all.

What are you thoughts on the readings @TonyM is seeing, and his tester telling him the battery is OK?
I would guess my own vehicle would fail to start at those lower voltages, but my own vehicle's electronics
and starting system are quite different. I have never seen lower than 12.2v, and when it failed I was too
busy arranging a replacement to see the voltage on the failed battery.

 

[lufa6977]

Thanks for your thoughts!

My only experience with automotive batteries is replacing one of mine when it fails. And I have the battery tester I linked
above, but have never used it myself.

Perhaps taking the vehicle to the dealer or other, with reliable test equipment, is the better idea after all.

What are you thoughts on the readings @TonyM is seeing, and his tester telling him the battery is OK?
I would guess my own vehicle would fail to start at those lower voltages, but my own vehicle's electronics
and starting system are quite different. I have never seen lower than 12.2v, and when it failed I was too
busy arranging a replacement to see the voltage on the failed battery.

For some years, we had a good lifespan from most of our commercial, semi-truck-sized batteries. It takes two people to lift or carry the battery. Someone decided we needed to do the 'toaster' test monthly. It took maybe six or so months before we started experiencing an unexpected increase in battery failures. Areas that stopped the toaster test saw a decrease in battery failures.

Tony's first image shows a good charge test with no ripple, which means the alternator is working correctly. The second test looks good. The only concerning thing I see on the third test is that the IR is a hair high. Max IR on a 290 CCA would probably be less than 10 mOhms; his battery is just a hair over that, so not really bad at all.

12.4 VDC I would expect to be an average resting voltage. The overnight voltage drop seems a bit extreme, so perhaps a parasitic drain, or the camera has been recording much of the night?

 

[Finnegan]

My vehicle, plain old ICE Ram 5.7L V8 with CANBUS and more "modules" than I can count
does not suffer any low voltage supply event.
My driveway features a household outlet 15 feet from where I park, so I installed a little
Noco 2a maintainer. I am also retired and the truck sits a lot, and even when driven it
sees only short drives.

BTW, I have a couple friends I worked with who would describe their careers exactly the same
way you did. I have to ask, was this "domestic telecom"? Our region was Mid-Atlantic and we
spent the majority of our time in and throughout Virginia. Arlington to Tidewater to Roanoke
and everything in-between. A truly beautiful state.
/end of my off-topic 😉

 

[lufa6977]

Yep, domestic telecom in the same area as you describe. USAF prior to that. Background in ET, Radio, Switching, SecComs, Fiber, analog and digital, and software. Old school, new school, retired, living well. 🙂

 

[Hack_man]

Before my retirement, one of my responsibilities was DC power plants and Diesel Generators as backup to commercial AC. Experience taught us that 'toaster' type load testers were best avoided. They put unnecessary strain on a battery and were more prone to damaging it than not. It is better to test a car battery with an analyzer that measures capacity percentage, life span, internal resistance, cold-crank amps, etc.

A car starter typically draws 100-200A and a battery load tester 100 A so how can it cause battery damage? You shouldn't be loading it for more than a few seconds starting or testing.
I'm wondering if the load tester you used drew much higher current than the typical DIY tester or maybe for a longer pulse duration.

 

[lufa6977]

A car starter typically draws 100-200A and a battery load tester 100 A so how can it cause battery damage? You shouldn't be loading it for more than a few seconds starting or testing.
I'm wondering if the load tester you used drew much higher current than the typical DIY tester or maybe for a longer pulse duration.

I don't know. Perhaps the toaster does a deeper draw than a starter?

I only know what happened when we used them, and the benefit of not using one. A battery analyzer, such as the one used by the OP, or something like one of the Midtronics that I used, provides far better testing with no possible damage to the battery.

 

[Hack_man]

Well I can't argue with the results from the Topdon BT50. Some of the cheaper electronic battery testers can be duds. Amazon reviews for this $33 unit are excellent and Project Farm tested the BT100 and BT200 with Excellent results.
It's tempting to add this to my Toaster style tester.

I'd be suspicious of parasitic drain, maybe test voltage drops on fuses to see if anything turns up to be suspicious. Just keep in mind the car probably takes a while to go to sleep and into low current mode after being turned off, I'm not sure how long.