Car Battery Charge Time Calculator
Calculate how long it will take to charge a car battery based on capacity (Ah), charger output (amps), and current state of charge.
A car battery that won’t start your vehicle is one of the most common roadside problems. Understanding how battery charging works helps you plan ahead — whether you’re using a trickle charger overnight, a standard home charger, or a fast charger.
Battery Capacity: Amp-Hours (Ah)
Battery capacity is measured in Amp-hours (Ah). A 60 Ah battery can theoretically deliver 1 amp for 60 hours, or 60 amps for 1 hour. Most passenger car batteries range from 40–100 Ah. Truck and SUV batteries are often 95–200 Ah.
Common Battery Sizes
| Vehicle Type | Typical Capacity |
|---|---|
| Small car (e.g., Civic) | 40–55 Ah |
| Mid-size sedan | 55–70 Ah |
| SUV / Crossover | 70–90 Ah |
| Truck / Van | 90–120 Ah |
| Diesel truck | 100–200 Ah |
Charge Time Formula
Charge time (hours) = Battery capacity (Ah) × Depth of discharge ÷ (Charger amps × Efficiency)
Charger efficiency accounts for heat loss and is typically 85–90%. A factor of 1.1 is commonly used:
Charge time = (Ah needed) ÷ Charger amps × 1.1
Charger Types and Speeds
| Charger Type | Typical Output | Best For |
|---|---|---|
| Trickle charger | 1–2A | Long-term maintenance, overnight |
| Standard home charger | 4–10A | Overnight charging, fully discharged |
| Fast charger | 15–40A | Faster charging, need to monitor temperature |
| Jump starter pack | High burst | Emergency starting only, not for full charge |
State of Charge (SoC)
A battery that’s 50% discharged needs half the charging of a fully flat one. If you left your lights on for 2 hours, the battery may only be 20–30% discharged and can be charged in a few hours. A fully flat battery from prolonged disuse takes longer and may be sulfated (unable to hold full charge).
Battery Voltage Reference
| Voltage | State of Charge |
|---|---|
| 12.7V+ | Fully charged |
| 12.4V | ~75% charged |
| 12.2V | ~50% charged |
| 12.0V | ~25% charged |
| 11.9V or below | Fully discharged (needs immediate charging) |
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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