Alignment Diagnostics and Fleets
Car Battery State-of-Health Calculator
Compare measured battery capacity and cranking performance with ratings. Different test methods do not measure identical battery characteristics.
Values used in the formula
Enter current information for Car Battery State-of-Health and leave unrelated adjustments outside the form.
From measurements to output
Compare measured battery capacity and cranking performance with ratings — use the result to decide what to inspect next, not to skip the inspection.
Different test methods do not measure identical battery characteristics — that condition defines when conservative state of health is comparable with another result.
The Rated battery capacity entry represents new-battery amp-hour rating — before calculating, identify whether the reading is taken at the source, charger, battery, or accessory.
Measured battery capacity: Capacity measured under a compatible test — a compatible entry should identify whether the reading is taken at the source, charger, battery, or accessory.
For Rated cold-cranking amps, use the quantity described as new-battery CCA rating — in the vehicle record, identify whether the reading is taken at the source, charger, battery, or accessory.
Measured cold-cranking amps is defined here as conductance or load-test estimate — keeping that definition intact requires you to use the same loaded condition for every weight and retain the scale ticket or rating source.
In “conservative SOH = lower of measured/rated capacity and measured/rated CCA,” the printed units define how each term is interpreted.
No term beyond rated battery capacity, measured battery capacity, rated cold-cranking amps, and measured cold-cranking amps is introduced in “conservative SOH = lower of measured/rated capacity and measured/rated CCA.”
From output to vehicle decision
Conservative state of health answers “Compare measured battery capacity and cranking performance with ratings.” The additional displays, Capacity state of health and CCA state of health, are a different view of the same entered measurements.
Temperature, state of charge, surface charge, and tester configuration affect results — when that condition changes, compare separate calculator runs instead of blending the inputs.
Because different test methods do not measure identical battery characteristics, a disagreement between conservative state of health and an outside reference should trigger a review of rated battery capacity and measured cold-cranking amps.
Boundaries of the result
A sensor or comparison value can narrow an investigation, but it cannot identify the failed part without the specified physical tests — for measured cold-cranking amps, the page specifically expects conductance or load-test estimate.
A concrete calculation
The displayed form begins with Rated battery capacity = 70 Ah, Measured battery capacity = 52 Ah, Rated cold-cranking amps = 700 A, and Measured cold-cranking amps = 560 A.
The arithmetic check is complete when the page displays Conservative state of health = 74.3%, Capacity state of health = 74.3%, and CCA state of health = 80.0%.
When the vehicle decision also requires you to calculate use of available fleet capacity, calculate it independently with the Fleet Vehicle Utilization.
Common issues with this calculation
What measurement source fits Rated battery capacity when it represents new-battery amp-hour rating?
Because rated battery capacity represents new-battery amp-hour rating, use a source tied to the exact vehicle, component, and operating period described by the other fields.
How does the warning “Different test methods do not measure identical battery characteristics” affect Conservative state of health?
The condition “Different test methods do not measure identical battery characteristics” is not corrected automatically by the numeric inputs, so create a separate car battery state-of-health case when it changes.
What assumption is expressed by “conservative SOH = lower of measured/rated capacity and measured/rated CCA”?
In “conservative SOH = lower of measured/rated capacity and measured/rated CCA,” rated battery capacity and measured battery capacity are treated as parts of one vehicle case.