{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"battery-charge-time"},"result":{"entity_type":"calculator","id":"battery-charge-time","calculator_id":"battery-charge-time","canonical_url":"https://tttkmbb.com/engineering/battery-charge-time","name":"Battery Charge Time Calculator","title":"Battery Charge Time Calculator – Hours to Charge from Capacity, Charger Current and Efficiency, with C-Rate","category":"engineering","category_name":"Engineering & Automotive","tool_name":"estimate_battery_charge_time","featured_mcp_tool":false,"description":"Estimates the time to charge a battery from its capacity in Ah, the charger current, the charge efficiency (default 85 %) and the starting state of charge, and reports the charging C-rate.","use_when":"You need to know how long a phone, e-bike, car or solar battery takes to charge with a given charger current, or the C-rate that a charger imposes.","do_not_use_when":"You need the runtime of a battery under load (use battery-runtime) or an exact lithium-ion CC/CV profile (the constant-voltage tail makes the last 20 % slower than this linear estimate).","inputs":[{"name":"capacity_ah","label":"Battery capacity","type":"number","unit":"Ah","required":true,"exclusive_min":0,"description":"Rated capacity in ampere-hours (mAh ÷ 1000, e.g. 2500 mAh = 2.5 Ah).","example":2.5},{"name":"charge_current_a","label":"Charger current","type":"number","unit":"A","required":true,"exclusive_min":0,"description":"Charging current delivered to the battery in amperes (for a USB charger, its rated output current).","example":1},{"name":"charge_efficiency_percent","label":"Charge efficiency","type":"number","unit":"%","required":false,"default":85,"min":30,"max":100,"description":"Fraction of the charger's output stored as charge: ≈ 85 % for lead-acid and simple chargers, 95–99 % coulombic efficiency for lithium-ion (losses then come from the CV tail).","example":85},{"name":"start_charge_percent","label":"Starting state of charge","type":"number","unit":"%","required":false,"default":0,"min":0,"exclusive_max":100,"description":"State of charge at the start; 0 for a fully discharged battery.","example":0}],"outputs":[{"name":"charge_needed_ah","label":"Charge to add","type":"number","unit":"Ah","decimals":3,"description":"capacity_ah × (100 − start_charge_percent) / 100."},{"name":"charge_time_hours","label":"Charge time","type":"number","unit":"h","decimals":3,"description":"charge_needed_ah / (charge_current_a × efficiency)."},{"name":"charge_time_formatted","label":"Charge time (h:mm:ss)","type":"string","decimals":4,"description":"Charge time as hours:minutes:seconds."},{"name":"ideal_charge_time_hours","label":"Charge time at 100 % efficiency","type":"number","unit":"h","decimals":3,"description":"charge_needed_ah / charge_current_a."},{"name":"c_rate","label":"C-rate","type":"number","unit":"C","decimals":3,"description":"charge_current_a / capacity_ah; 1C charges the nominal capacity in one hour."},{"name":"c_rate_description","label":"C-rate assessment","type":"string","decimals":4,"description":"Typical interpretation of the C-rate for consumer cells."}],"input_schema":{"type":"object","properties":{"capacity_ah":{"description":"Rated capacity in ampere-hours (mAh ÷ 1000, e.g. 2500 mAh = 2.5 Ah). Unit: Ah.","type":"number","exclusiveMinimum":0,"examples":[2.5],"x-unit":"Ah"},"charge_current_a":{"description":"Charging current delivered to the battery in amperes (for a USB charger, its rated output current). Unit: A.","type":"number","exclusiveMinimum":0,"examples":[1],"x-unit":"A"},"charge_efficiency_percent":{"description":"Fraction of the charger's output stored as charge: ≈ 85 % for lead-acid and simple chargers, 95–99 % coulombic efficiency for lithium-ion (losses then come from the CV tail). Unit: %.","type":"number","minimum":30,"maximum":100,"default":85,"examples":[85],"x-unit":"%"},"start_charge_percent":{"description":"State of charge at the start; 0 for a fully discharged battery. Unit: %.","type":"number","minimum":0,"exclusiveMaximum":100,"default":0,"examples":[0],"x-unit":"%"}},"additionalProperties":false,"required":["capacity_ah","charge_current_a"]},"output_schema":{"type":"object","properties":{"charge_needed_ah":{"description":"capacity_ah × (100 − start_charge_percent) / 100. Unit: Ah.","type":"number","x-unit":"Ah"},"charge_time_hours":{"description":"charge_needed_ah / (charge_current_a × efficiency). Unit: h.","type":"number","x-unit":"h"},"charge_time_formatted":{"description":"Charge time as hours:minutes:seconds.","type":"string"},"ideal_charge_time_hours":{"description":"charge_needed_ah / charge_current_a. Unit: h.","type":"number","x-unit":"h"},"c_rate":{"description":"charge_current_a / capacity_ah; 1C charges the nominal capacity in one hour. Unit: C.","type":"number","x-unit":"C"},"c_rate_description":{"description":"Typical interpretation of the C-rate for consumer cells.","type":"string"}}},"formula":"charge_time_hours = capacity_ah × (100 − start_charge_percent) / 100 / (charge_current_a × charge_efficiency_percent / 100); c_rate = charge_current_a / capacity_ah","method":"Linear approximation. Lithium-ion chargers switch from constant current to constant voltage at about 70–80 % charge, so the final portion takes longer than the current alone suggests; lead-acid absorption charging behaves similarly.","sources":[{"name":"Battery University – BU-409: Charging Lithium-ion","url":"https://batteryuniversity.com/article/bu-409-charging-lithium-ion","type":"reference","retrieved_at":"2026-09-24"},{"name":"Battery University – BU-402: What is C-rate?","url":"https://batteryuniversity.com/article/bu-402-what-is-c-rate","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Battery charger","url":"https://en.wikipedia.org/wiki/Battery_charger","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"2,500 mAh phone battery on a 1 A charger","inputs":{"capacity_ah":2.5,"charge_current_a":1},"expected":{"charge_needed_ah":2.5,"charge_time_hours":2.941,"charge_time_formatted":"2:56:28","ideal_charge_time_hours":2.5,"c_rate":0.4},"url":"https://tttkmbb.com/api/v1/calculate/battery-charge-time?capacity_ah=2.5&charge_current_a=1"},{"name":"100 Ah battery from 50 % at 10 A","inputs":{"capacity_ah":100,"charge_current_a":10,"start_charge_percent":50},"expected":{"charge_needed_ah":50,"charge_time_hours":5.882,"c_rate":0.1},"url":"https://tttkmbb.com/api/v1/calculate/battery-charge-time?capacity_ah=100&charge_current_a=10&start_charge_percent=50"}],"faq":[{"q":"Which current do I enter for a USB charger?","a":"The charger's rated output current (e.g. 2 A) only if the device draws it; most phones limit charging to their own maximum and the charge current falls in the CV phase."},{"q":"What is a safe C-rate?","a":"Standard lithium-ion cells are rated for 0.5–1C charging; lead-acid is usually charged at 0.1–0.3C. Higher rates need cells and chargers designed for fast charging."}],"tags":["battery charge time","charging time calculator","how long to charge","c-rate","ah charger amps"],"related":[{"calculator_id":"battery-runtime","reason":"How long the charged battery will run a load."},{"calculator_id":"solar-panel-output","reason":"Daily solar energy available for charging."},{"calculator_id":"electric-power","reason":"Charger power and energy cost from voltage and current."}],"links":{"html":"https://tttkmbb.com/engineering/battery-charge-time","markdown":"https://tttkmbb.com/engineering/battery-charge-time.md","json":"https://tttkmbb.com/engineering/battery-charge-time.json","api":"https://tttkmbb.com/api/v1/calculate/battery-charge-time","schema":"https://tttkmbb.com/api/v1/calculators/battery-charge-time","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:58:13Z"}