EV Charge Time & Cost Calculator mechanism

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

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