You can test a battery if you go under the hood and connect up the right meter to measure the battery integrity but why can’t a modern car employ the technology easily? (Or maybe it does and I need a new car)
In: Engineering
My battery had some cells die and it dropped to 8 volts. There was definitely warning icons in the dash telling me the battery needed inspection
Even a bad battery can show you 12v. But as soon as a load is present, drop to 8v.
When you test the battery in the shop, a big load is put on, for example some heating coils (inside the tester). It should be hard to automate this and not overstrain the battery.
They don’t lack this. Every car for many many years has a volt meter and most have a warning light or message if charging gets too low.
Batteries in traditional (i.e. gasoline-powered internal combustion engine) cars are only used for (a) powering the starter motor to start the engine or (b) running electrical features (e.g. radio, lights) when the engine isn’t running. Car batteries are automatically re-charged by the alternator, which uses power from the engine to generate electricity while the engine is running, both for re-charging the battery and running electrical features of the car.
Traditional car batteries don’t really store that much energy, since their primary purpose is only to power the starter motor that gets the combustion engine running. Basically, they need to put out one big boost to start the engine, then they get automatically re-charged once the engine is humming. So there are two reasons your car battery will die:
1. The alternator is failing to do it’s job, so, while driving, anything that relies on electricity like lights or windshield wipers or radio will drain the battery instead of getting electricity from the alternator.
2. The engine isn’t running, but something else is draining the battery. E.g. lights are left on while the car isn’t running or there’s a short somewhere in the electrical system.
Most modern cars (at least in the US) *have* an alternator/battery-warning dashboard light that comes on when the alternator is failing to provide sufficient power to re-charge the battery. That takes care of #1.
However, #2 occurs when the engine isn’t running … which usually means you aren’t in the car. Since a car battery doesn’t store all that much energy on its own, if you’re away from the car for a few hours with something draining the battery, it’s not going to start when you get back to the car. (And if it didn’t drain the battery enough to prevent the car from starting, then the battery will be re-charged by the engine as soon as you start driving again.)
So, as long as your alternator is working correctly, your battery generally won’t have issues. Cars have warning lights to let the driver know if the alternator is failing. But if your battery loses its charge for some other reason (e.g. human error or electrical system problems), it’s going to go from a usable charge to insufficient charge to start the car pretty quickly *while you’re not driving and not in the car*, so a warning light isn’t any help.
TL;DR: if you leave your car lights on overnight, a warning light that you’re draining the battery isn’t much use while you’re asleep in bed.
Many cars measure voltage at turn-on and can signal you. The most important test, trying to start the car, already has a “warning”, wken the car doesn’t start. Without a more sophisyicated test, you can’t tell “low charge” from “bad battery”. A bad battery is pretty obvious, but predicting it doesn’t work unlesss people are going to replace t_eir battery when the car says “battery failure within a month”.
There’s a battery light that pops up when battery voltage is low on some cars. Diagnosing lead-acid battery health is not as simple as measuring voltage, it can be near full voltage and go down super low when you actually try and draw power. You’re required to change batteries often enough that it shouldn’t be a problem, but many people only change them when they die leaving them in a field.
I posted a somewhat similar question a few days ago and everyone acted like I was stupid. Maybe I worded it wrong but I was basically saying the same thing wondering how come we can’t see percent of the car’s battery.
Why can’t gas-powered cars have battery statuses like a cell phone or electric car with a percentage on the dash cluster?
byu/30somethingmale inAskReddit
You give the example of using multimeter to check your battery, but that doesn’t actually tell you anything about battery health. A battery can show 12v on a multimeter but not actually have enough capacity to start an engine. You should check voltage drop under load, you’ll notice as a battery gets weaker the voltage will dip more when it is put under load like starting the engine. This is the idea of those battery capacity testers you can buy in store. They just have a big resistor in them that draws a huge load on the battery and you check what the voltage drops to.
If you want to really check battery health you can do a capacity check. They aren’t commonly done on vehicles but often done on aircraft. Basically you charge the battery fully, put a known load on the battery, and then time how long it takes to get below a certain voltage.
You then compare that to the manufacturers numbers to see if your battery is low on capacity or not.
It’s not done on vehicles because in a vehicle a battery is primarily there to start the engine, if the engine doesn’t start you know it’s bad but no harm done besides the inconvenience.
It’s done often on aircraft because the battery is there to provide emergency power in the event of an alternator/generator going bad. You don’t want to be flying through clouds with no visibility relying on your instruments for navigation and find out your battery is shot when you alternator goes out.
Here is a video from Concorde about battery capacity testing.
Because batteries are quite good.
My saturn had a 1.2 kW starter. A healthy battery dips to 10 volts during cranking, so that’s 120 amps demanded. The battery for it was rated for 650 cold-cranking amps. To pass the test it has to supply 650 amps at 32 degrees *for thirty seconds*. It could do more amps for the three seconds it actually takes to start the car.
One could test the battery annually and see a gradual decline, but it would still bump that starter over nicely. If it declined on a parabolic curve, which I bet it does, the fall-off would be dramatic by the point the car stopped starting.
In the old days, starters were direct-drive, weighed 50 lbs, were 10 inches long, 5 inches in diameter, and guzzled amps, so you would in fact note the decay earlier via slower cranking. You’d have more warning because you were on a flatter part of the curve. Modern starters use gear reduction drives which draw fewer amps, making the failure point more binary.
It’s a miracle we’re still getting batteries as big as we still do. This adds a smidge of reliability, and capacity to run things like the radio memory and remote keyless entry sensors if the car is parked for a week. Companies like Honda put skinny bullshit batteries in some of their cars to save fuel but the trays will have holes for bigger replacements.
The technical people answering are technically correct, that a voltmeter would indicate the voltage of a battery, but they’re missing what OP is after: when won’t a battery work anymore? In other words, they are wondering “why can’t I know the health of my battery?”
With car batteries (the 12V lead acid type) the voltage isn’t really a good indicator of health. An old dead battery can read ~12V just fine. It would likely power most lights and equipment, too. The real test of health comes when trying to start the engine; the “load” test. An old battery can read 12V until asked to turn the starter, then immediately drops to an unusable voltage.
The simple answer is that traditional 12V car batteries do not have the sophisticated tech to indicate their health like, say, laptop batteries. Nor is there a good way to test the health except for hooking the battery to a load, which isn’t an easy thing to build into a car’s circuitry. Basically, starting the engine IS the load test.
Edit: To all those asking why a load tester couldn’t be added into the hardware or software of a car: it could. Nearly anything is possible with time and money. But I agree with the comments from those in the industry; it comes down to three basic things:
1) Added cost (automotive margins are very thin)
2) Added complexity and engineering effort for nearly no return (exactly who would truly want this?)
3) Service side (auto companies do not wish customers to have to think about maintenance beyond knowing to take the vehicle in when the light turns on)
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