Source: https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/mechanism/

instrument mechanism / verified-clean

# EV Charge Time & Cost Calculator mechanism

The inspectable method record for EV Charge Time & Cost Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The arithmetic formulas are conditionally standard, but the specification must explicitly distinguish battery energy added from grid energy consumed and define whether charger_kw is grid-side or battery-side power. The honest label correctly states that actual charging time varies because charging curves and operating conditions are not modeled.

- energy_kwh = battery_kwh × (target% − start%) / 100 / charge_efficiency is correct for energy drawn from the grid, assuming charge_efficiency is the total charging efficiency.

- The stated output 'energy added' is ambiguous: energy stored in the battery is battery_kwh × (target% − start%) / 100, while the supplied energy_kwh formula includes losses and therefore represents grid energy consumed.

- time_hr = energy_kwh / charger_kw is correct only if charger_kw is the charger-side power corresponding to the same energy basis as energy_kwh. If charger_kw is battery-side delivered power, time should instead use battery energy divided by charger_kw, subject to the efficiency convention.

- cost = energy_kwh × rate_per_kwh is correct when rate_per_kwh is the price per kWh of grid energy consumed.

## Units and conventions

- battery_kwh and energy_kwh are in kWh.

- charger_kw is in kW, so energy_kwh / charger_kw produces hours.

- start% and target% are percentage points from 0 to 100, not decimal fractions.

- charge_efficiency is a dimensionless fraction, such as 0.90 for 90%, and represents total grid-to-battery efficiency.

- rate_per_kwh is currency per grid kWh.

- The test vectors treat charger_kw as grid-side input power and energy_kwh as grid energy consumed.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "battery_kwh": 60,
    "start_percent": 20,
    "target_percent": 80,
    "charger_kw": 11,
    "rate_per_kwh": 0.3,
    "charge_efficiency": 0.9
  },
  "expected_outputs": {
    "energy_added_kwh": 36,
    "energy_kwh": 40,
    "time_hr": 3.6363636364,
    "cost": 12
  },
  "working": "Battery energy added = 60 × (80 − 20) / 100 = 60 × 0.60 = 36 kWh. Grid energy = 36 / 0.90 = 40 kWh. Time = 40 / 11 = 3.6363636364 hr. Cost = 40 × 0.30 = 12.00 currency units."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The calculator has a definite undefined-result break when charger_kw is zero. It also needs validation for target_percent below start_percent and an explicit charge-efficiency input convention; otherwise it can return negative or physically nonsensical results.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`