Calcgrid

EV Charging Time Calculator

estimate_ev_charging_time

Read-onlyIdempotent

Use this when you want to know how long an EV needs on a home wallbox, a public AC post or a DC fast charger to reach a target charge, or what the session costs at a given electricity price. Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery.

Do not use this when you need a battery's charge time from ampere-hours and charger current (use battery-charge-time) or the driving range the added energy gives (use ev-range-efficiency); DC fast charging above about 80 % tapers strongly and takes longer than this constant-power estimate. What it computes: Estimates how long an electric vehicle takes to charge between two states of charge from its battery capacity, the charger power (capped by the onboard charger for AC charging) and the charging efficiency, plus the energy drawn from the grid and its cost. Inputs: battery_capacity_kwh (number, kWh); start_percent (number, %, optional); target_percent (number, %, optional); charger_power_kw (number, kW); max_onboard_charger_kw (number, kW, optional); charging_efficiency_percent (number, %, optional); electricity_price_per_kwh (number, per kWh, optional). Complete JSON argument examples: {"battery_capacity_kwh":75,"start_percent":20,"target_percent":80,"charger_power_kw":7,"charging_efficiency_percent":90,"electricity_price_per_kwh":0.3} | {"battery_capacity_kwh":60,"start_percent":10,"target_percent":100,"charger_power_kw":11,"max_onboard_charger_kw":7.4} Outputs: energy_added_kwh [kWh], energy_from_grid_kwh [kWh], effective_power_kw [kW], charging_time_hours [h], charging_time_text, cost, range_note. Formula: energy_added_kwh = battery_capacity_kwh × (target_percent − start_percent) / 100; energy_from_grid_kwh = energy_added_kwh / (charging_efficiency_percent / 100); effective_power_kw = min(charger_power_kw, max_onboard_charger_kw); charging_time_hours = energy_from_grid_kwh / effective_power_kw; cost = energy_from_grid_kwh × electricity_price_per_kwh Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/ev-charging-time with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/energy/ev-charging-time.md

Input Schema

TableJSON Schema

Name	Required	Description
`start_percent`	No	State of charge at the start of the session. Unit: %.
`target_percent`	No	State of charge to reach; must be higher than start_percent. Unit: %.
`charger_power_kw`	Yes	Power the charging point delivers: 1.4–2.3 kW household socket (Level 1), 7–22 kW wallbox / AC post (Level 2), 50–350 kW DC fast charger. Unit: kW.
`battery_capacity_kwh`	Yes	Usable battery capacity in kilowatt-hours (e.g. 40, 60, 75, 100). Unit: kWh.
`max_onboard_charger_kw`	No	Optional maximum AC charging power of the car's onboard charger (commonly 7.4 or 11 kW); the effective power is the lower of the two. Omit for DC charging. Unit: kW.
`electricity_price_per_kwh`	No	Optional price per kWh in your currency for the cost of the session (grid energy × price). Unit: per kWh.
`charging_efficiency_percent`	No	Share of grid energy stored in the battery; 85–92 % is typical for AC charging (onboard charger and battery losses). Unit: %.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`links`	No
`result`	Yes
`request`	Yes
`sources`	No
`success`	Yes
`version`	No
`freshness`	No
`timestamp`	Yes
`next_actions`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 26, 2026

addedInput schema / examples

Added value: +[
+  {
+    "battery_capacity_kwh": 75,
+    "charger_power_kw": 7,
+    "charging_efficiency_percent": 90,
+    "electricity_price_per_kwh": 0.3,
+    "start_percent": 20,
+    "target_percent": 80
+  },
+  {
+    "battery_capacity_kwh": 60,
+    "charger_power_kw": 11,
+    "max_onboard_charger_kw": 7.4,
+    "start_percent": 10,
+    "target_percent": 100
+  }
+]

AddedSep 25, 2026
RemovedSep 25, 2026
First observedSep 25, 2026

TDQS

A4.6/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, and non-destructive hints. The description adds behavioral context beyond annotations: it is a constant-power estimate, mentions DC fast charging taper, and discloses the cost calculation. It does not contradict any annotation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is long but organized into clear sections: usage, exclusions, computed values, inputs, examples, outputs, formula, and REST fallback. The inputs list is redundant with the schema, but the rest earns its place. Front-loading the usage conditions is effective.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex 7-parameter calculator with an output schema, the description covers everything an agent needs: when to use, what it computes, all parameters, example JSON, output names, the exact formula, a REST fallback, and a docs link. Nothing critical is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and each parameter is already well-described. The description adds value by explaining the relationships between parameters (e.g., effective_power = min(charger_power_kw, max_onboard_charger_kw)) and the cost formula, which gives the agent a deeper understanding of how inputs affect outputs.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with explicit use cases (home wallbox, AC post, DC fast charger) and states exactly what it computes (charging time, energy, cost). It distinguishes from sibling tools by name (battery-charge-time, ev-range-efficiency), leaving no ambiguity about scope.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides clear when-to-use and when-not-to-use conditions, explicitly naming the alternative tools for battery charge time and driving range. It also warns about DC fast charging taper, which helps the agent select the tool appropriately.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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