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

instrument implementation / implementation-contract

# EV Charge Time & Cost Calculator implementation

A source-bound implementation contract for EV Charge Time & Cost Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t4-163

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "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."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/ev-charge-time-cost-calculator/mechanism/>)[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`