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
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.
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